US 1592979

I'll search for the specific patent number and any related litigation activity.

Let me check specifically for any CAFC 2026 docket activity and USPTO records for this patent number.

US Patent 1,592,979 — "Measuring Device"

Bottom line: I confirmed the patent's identity and bibliographic data against the Google Patents full text (already supplied in your message) and cross-checked against FreePatentsOnline's record for the same number. I found no CAFC 2026 docket activity involving this patent, and for reasons explained below such activity is effectively impossible.

Bibliographic record

⚠ Identifier discrepancy (not auto-corrected): Google Patents' bibliographic data lists the application as US 382,031 filed 1920‑05‑17, while the OCR of the printed specification reads "Serial No. 382,081." I am reporting both as found; the bibliographic field is more likely authoritative, but I cannot resolve the OCR conflict with certainty.

⚠ No formal abstract. This is a 1926 document, predating the modern abstract requirement. There is no separately labeled "Abstract." The specification opens with a set of "My invention relates to…" paragraphs that effectively serve that function, and Google Patents reproduces those under a "Definitions" heading. Any abstract quoted below is a synthesis, not verbatim statutory text.

Abstract (synthesized from the specification)

The patent discloses an electrical measuring device in which a sensitive/measurement-effecting element (e.g., a platinum electrode disk, a thermocouple, or a resistance element) is mounted on the end of a removable plug structure. The plug has an insulating body (porcelain or similar fragile insulating material) with cylindrical end portions and a larger-diameter middle portion forming shoulders; a metal casing surrounds one end and is threaded for screwing into a supporting structure. A conductor passes axially through the insulating body and a pocket, is potted in insulating material (wax) inside the casing, and terminates outside the casing for connection to a conductor leading to measuring apparatus (e.g., a Wheatstone bridge). The plug may be combined with a supporting plate/diaphragm and a perforated protecting casing that shields the sensitive element from impact while admitting the fluid, liquid, or solution under test. Two plugs may be mounted in a common diaphragm to measure liquid conductivity, or the electrode disks may be replaced by thermocouple elements or a resistance wire.

Independent claims — plain-language overview

All six claims are independent. There are no dependent claims in this patent. (Note: the OCR of claim 1 is garbled and appears to be missing a phrase — see below.)

Claim 1 — Multi-plug assembly with plate, conduit and casing. An electrical measuring apparatus combining a plate member; a conduit extending perpendicularly(?) from one side; a casing extending from the other side; multiple plug structures carried by the plate and projecting into the casing; an electrode on each plug; and electrical conductors running through the conduit and the plugs to the electrodes. Caveat: the OCR text of claim 1 begins "comprising the combination with a plate memof said plate member…" and jumps straight to "a casing extending from the other side," omitting the "conduit extending from one side" antecedent that appears in claim 6. The claim as printed in Google Patents is defective/garbled at that point and I cannot reconstruct it with certainty.

Claim 2 — The detachable plug unit itself (the core structural claim). A detachable unit comprising: an insulating member with substantially cylindrical end portions, one end portion having a pocket; an opening through the insulating member communicating with the pocket; a metallic plug member surrounding that one end portion and projecting beyond it, screw-threaded on the projecting end; an electrical conductor extending through the opening, pocket, and projecting end for connection to measuring apparatus; insulating material filling the pocket and projecting end and surrounding the conductor therein; and a measurement-effecting element on the other end of the insulating member electrically connected to the conductor. (The printed claim reads "measurement-enacting" element, almost certainly an OCR/typographical rendering of the coined term "measurement-effecting" element defined later in the specification.)

Claim 3 — Conduit + supporting member + plug + protecting casing. Apparatus combining a conduit; a supporting member on the conduit's end; plug structure carried by that member; a protecting casing supported on the conduit and surrounding the plug structure; and a measurement-effecting device on the plug, enclosed within the casing. (Claim 3 uses "condult" for conduit and "device" rather than "element" — reported as printed.)

Claim 4 — Detachable unit with protecting casing and conduit. A supporting member carrying a detachable unit of plug structure; a measurement-effecting element on an end of the plug; a conductor connected to the element and passing through the plug for external connection; a protecting casing surrounding both the plug and the element; and a conduit supported on the supporting member.

Claim 5 — Same combination, expressed as a two-sided assembly. A supporting member with a detachable plug-structure unit; a measurement-effecting element mounted on the plug; a protecting casing projecting from one side of the supporting member around the plug; a conduit projecting from the other side; and a conductor running through the conduit for external connection, connected to the element through the plug structure.

Claim 6 — Plate + perpendicular conduit + perforated casing (the narrowest/most specific). Combines a plate member; a conduit extending perpendicularly from one side; a cylindrical casing extending perpendicularly from the other side, with a plurality of orifices adjacent the plate; openings in the plate; a plurality of plug structures each secured at one end in a plate opening and projecting into the casing; electrodes on the projecting ends; and conductors through the conduit and plugs connected to the electrodes. This claim adds the perforation limitation expressly (spec: perforations 41 admitting fluid to the electrodes while the casing shields them from mechanical contact).

Notable coined terminology. The specification expressly defines a generic term for the sake of claim brevity: "the aforesaid responsive or sensitive elements, such as 27, 27¹, T, R, etc., notwithstanding their characteristically different actions or modes of use, are generically referred to as measurement-effecting elements." This is a deliberate genus-coining move so that one claim set covers electrodes, thermocouples, and resistance elements.

CAFC / litigation search — negative result

• No CAFC 2026 docket entry, opinion, order, or scheduled argument was found for U.S. Patent 1,592,979, and none should be expected: the patent expired on or about July 20, 1943, and the U.S. Court of Appeals for the Federal Circuit did not exist until 1982 (Federal Courts Improvement Act of 1982, effective Oct. 1, 1982). The patent cannot be asserted in a 2026 infringement action, so it cannot generate a 2026 CAFC appeal on its own.

• Searches for "1592979" also returned numerous unrelated documents that must not be conflated with this patent, per your instruction to interpret identifiers literally:

  • GB 1592979 A — shaped articles of cross-linked fluorocarbon polymers (UK)
  • FR 1592979 A — plastics thermoforming apparatus (France)
  • DE 1592979 A1 — device for production of carbon black (Union Carbide)
  • EP 1592979 A2 — a separate European publication
  • RU 1592979 — a bone-tissue biopsy device
  • STF RE 1592979 — a 2026 Brazilian Supreme Court extraordinary appeal (unrelated)
  • FEI 83-1592979 — a Florida corporate filing number
  • A 2026 CAFC captioned case, WIPQTUS, INC. v. Samsung, is 2025-1596 — a coincidence of digits, not this patent

  None of these is U.S. Patent 1,592,979 or related to it.

Downstream citation footprint (for context)

Google Patents records roughly 10–11 third-party forward citations, almost all mid‑20th‑century conductivity-cell patents: US 2,525,754 (Hall Laboratories, "Conductivity cell," 1950); US 2,555,937 (Rosenthal, blood-clotting resistance, 1951); US 2,719,190 (Ethyl Corp., electrode assembly, 1955); US 2,769,140 (West Virginia Pulp & Paper, 1956); US 2,939,070 (Industrial Instruments, 1960); US 3,343,078 (Labindustries, 1967); US 3,939,401 (Beckman, "Conductivity cell electrode enclosure," 1976); US 4,071,816 (Arco Polymers, 1978); US 4,427,945 (Beckman, "Molded conductivity cell body," 1984); and WO 2017/079517 A1 / US 11,027,456 B2 (Shildan, Inc., ceramic composite). This confirms the patent's role as an early structural antecedent in the conductivity-cell / electrode-probe art.

Uncertainty flags

1. Application serial number — 382,031 (bibliographic) vs. 382,081 (printed OCR); unresolved.
2. Claim 1 text is incomplete in the available OCR (missing the "conduit extending from one side" antecedent present in claim 6); the true issued text should be verified against the USPTO Patent Public Search / PatentCenter scanned original or the Google Patents PDF.
3. "Measurement-enacting" (claim 2) vs. "measurement-effecting" (claims 3–5 and the specification's coined definition) — almost certainly the same term.
4. I did not retrieve an independent USPTO-hosted record beyond what is reflected in the Google Patents and FreePatentsOnline pages; I have no authoritative information beyond those sources, and I did not find any assignment/reassignment record beyond the original Leeds & Northrup ownership shown.

I'll search litigation-focused sources for this specific patent number.

Let me check a few more litigation-specific sources.

Litigation search — U.S. Patent 1,592,979

Bottom line: I found no litigation — no district court case, no ITC investigation, no PTAB proceeding, and no CAFC appeal — involving U.S. Patent 1,592,979. The correct answer to "list known litigation" is that none is known.

I am reporting this as a negative result on the sources checked, not as a certified global negative. My uncertainty is stated at the end.

What I searched and what came back

The only substantive records retrieved for this number are the patent documents themselves:

• Google Patents: https://patents.google.com/patent/[US1592979](/patent/US1592979)/en
• FreePatentsOnline: https://FreePatentsOnline.com/1592979.html — assignee Leeds & Northrup Co., application US38203120A, filed 05/17/1920, published 07/20/1926.

Google Patents' page for US1592979A contains no "Litigation" or "Related litigation" section — a field that Google Patents populates when it has case associations. Its only downstream record is a "Cited By" list of ~10–11 forward-citing patents, none of which indicates an enforcement action.

Why no litigation exists — structural reasons

1. The patent expired July 20, 1943 (anticipated expiration shown in the Google Patents legal-status record; term measured from the 1920 filing). A 2026 suit or appeal asserting it is legally impossible.
2. The CAFC did not exist until 1982. Appeals from district courts in 1926–1943 went to the regional U.S. Circuit Courts of Appeals (Third Circuit, for the Eastern District of Pennsylvania, where Leeds & Northrup sat). So even if a historical suit existed, it would not appear as a "CAFC" case, and it would not be captioned with a 2026 docket number.
3. Even if a pre-1943 suit existed, it would only be discoverable in print-era sources — the Federal Reporter (F.2d), the Federal Supplement (F. Supp., which began 1932), West's Decennial Digests, or the United States Patents Quarterly (USPQ, began 1929). Those volumes are largely not indexed in the free web sources I queried, and I did not retrieve them.

Identifiers I deliberately did not conflate with this patent

Per the operating rule to interpret identifiers literally, the following search hits contain the digits "1592979" but are different instruments and are not cited as litigation of US 1,592,979:

• GB 1592979 A — shaped articles of cross-linked fluorocarbon polymers (INIS record, published 15 Jul 1981; IPC C08J3/24)
• DE 1592979 A1 — burner/device for production of carbon black (Union Carbide)
• EP 1592979 A2 — portable detachable self-contained tracking unit for two-way satellite communication (US counterpart US 2004/0183673 A1) — cited as prior art in unrelated EP filings
• RU 1592979 — bone-tissue biopsy device (Kuvina et al., published 27.10.1995)
• RECURSO ESPECIAL Nº 1592979 — Brazilian Superior Tribunal de Justiça proceeding (2016/0075181-5); a litigation docket, but Brazilian and unrelated to U.S. patent 1,592,979
• FEI 83-1592979 — Florida corporate filing number (from the prior section)

None of these is a U.S. litigation involving the patent in suit.

Relationship to the previously generated section

This is consistent with, and completes, the earlier CAFC/litigation negative result. No contradiction with the earlier section. Two small notes for the record:

• The earlier section's bibliographic table is authoritative for this analysis (inventor Earl A. Keeler, of Norristown, PA; assignee Leeds & Northrup Co., Philadelphia). No litigation appears in that record either — the "Cited By" data is forward citation, not forward litigation.
• The prior section's unresolved serial-number conflict (bibliographic 382,031 vs. printed OCR 382,081) persists, but it does not change the litigation answer: neither number maps to any case record I found.

For each requested field

Uncertainty flags (stated explicitly, per your instruction)

1. I could not complete targeted Docket Alarm and PACER retrievals before the search budget was exhausted. Those are the two most likely places a historical or obscure case record would surface, so this is an incomplete-vendor check, not a fully exhaustive one.
2. Free web litigation databases are strongly biased toward post-1990 electronic records. A pre-1943 suit by Leeds & Northrup to enforce this patent could exist in print-only sources (F.2d, F. Supp., USPQ, Decennial Digests) and would be invisible to the searches I ran. I found no evidence of one; I cannot affirm there was none.
3. Google Patents does not display a litigation section for this patent, but Google Patents' litigation coverage for 1920s–1940s U.S. patents is effectively nil, so the absence of such a section is weak evidence rather than strong.
4. Nothing here should be read as an assertion about Leeds & Northrup's overall litigation history — that company was a prolific patentee and did litigate in later decades over other patents, none of which I tied to 1,592,979.

I'll verify the structured-block default with targeted searches before writing.

Proceedings overview

Zero AIA trial proceedings exist on U.S. Patent 1,592,979 — not "none found," but "none possible." The structured USPTO Open Data Portal block states no AIA trial proceedings are on file, and two independent web searches (2026-09-27) surfaced no IPR/PGR/CBM petition, institution decision, FWD, or appeal referencing this patent — only unrelated identifiers (the Brazilian Supreme Court appeal RE 1592979, EP 1592979 A from the Nageli fluoropolymer family, DE 1592979 A1, GB 1592979 A, FR 1592979 A, RU 1592979), none of which is U.S. 1,592,979.

The count therefore breaks down as: active 0 / claims invalidated 0 / claims sustained 0 / settled 0 / institution denied 0.

Bottom-line defensive posture: This is not a "hardened patent that survived IPRs" case, and it is not a "claims canceled by the Board" case either. It is a 1943-expired, public-domain patent that (a) was never subject to any AIA trial because the AIA trial regime did not exist during its enforceable life, and (b) cannot support a modern assertion at all. If a demand letter cites U.S. 1,592,979, the letter is defective on its face — the patent term ended 1943-07-20 (17 years from the 1926-07-20 issue date), and maintenance fees have not been payable since the pre-1981 regime. The patent's real current value is as prior art, not as an assertion weapon.

No proceedings to report

There are no proceeding sections to populate. Per the constraint against fabrication, I am not constructing placeholder captions, panel rosters, or dates. Specifically absent, and confirmed absent:

Why this is a structural certainty, not a search gap:

1. Temporal impossibility. Inter partes review became available 2012-09-16 (AIA § 6(c)(2)(A)). Post-grant review applies only to patents with an effective filing date on or after 2013-03-16 (AIA § 6(c)(2)(B)). Covered business method review existed only 2012-09-16 to 2020-09-16 and only for financial-services patents. U.S. 1,592,979 issued 1926-07-20 and its term expired 1943-07-20 — roughly 69 years before the earliest AIA trial date. No petition could have been, or can now be, filed within the AIA trial framework as applied to this patent.
2. No live controversy to support one. An IPR petitioner must be a real party in interest with a basis to challenge claims. Here there are no enforceable claims — the patent is expired and dedicated to the public. There is no infringement exposure to mitigate, so there is no rational petitioner and no § 315(b)/§ 315(a) posture to litigate.
3. Unrelated pre-AIA Board activity is also absent from the record. The predecessor tribunal (the Board of Patent Appeals and Interferences, and before it the Examiners-in-Chief) handled pre-AIA interferences under 35 U.S.C. § 135. Nothing in the Google Patents prosecution/assignment record supplied in your prompt shows an interference, reissue, or reexamination for this patent. I have not independently confirmed the complete paper file via USPTO PatentCenter — that is a residual gap, not a finding.

Strategic summary

Claim status: all of claims 1–6 are UNTESTED by any PTAB proceeding, and all of them are expired and unenforceable. No claim was canceled; no claim was sustained; no claim was construed by the Board. The six independent claims identified in the earlier section — claim 1 (multi-plug plate/conduit/casing assembly), claim 2 (the detachable plug unit, the structural core), claim 3 (conduit + supporting member + protecting casing), claim 4 (detachable unit + casing + conduit), claim 5 (two-sided casing/conduit combination), and claim 6 (plate + perpendicular conduit + perforated casing) — all lapsed with the term on 1943-07-20. For a defendant today, the relevant question is not "which claims survived IPR" but "why is anyone citing a 1926 patent at all."

Estoppel landscape: § 315(e)(2) is inapplicable and irrelevant. Estoppel attaches only to a petitioner who obtained an institution decision or FWD. Because no petition was ever filed, no petitioner, real party in interest, or privy is estopped from anything. Conversely — and more usefully — because there is no PTAB record, a defendant is not boxed into a "PTAB-said-so" invalidity theory. Every invalidity ground remains fully available in district court, and the usual § 101/§ 102/§ 103 battles are replaced by a much simpler defense: the asserted claims are expired, and the specification itself is citable prior art under § 102(a)(1) against any modern patent that claims the same plug-mounted measurement-element architecture. Note that the surviving forward-citation trail (US 2,525,754; US 2,555,937; US 2,719,190; US 2,769,140; US 2,939,070; US 3,343,078; US 3,939,401; US 4,071,816; US 4,427,945) shows the industry treated this disclosure as foundational antecedent art, which is exactly how it should be used now.

Pattern signals: none, and none possible. No repeat petitioner (no petitioner at all). No patent-owner appeal strategy — Leeds & Northrup never had an adverse Board decision to appeal, and the corporate entity's later history is outside this record. No defensive aggregator (Unified Patents, RPX, etc.) in the chain — aggregators challenge live patents, and there has been nothing to challenge here since 1943. The Shildan ceramic-composite family (WO 2017/079517 A1 / US 11,027,456 B2) appears in the forward-citation list only as a citation coincidence in the Google Patents "Cited By" table; it reflects no legal relationship to U.S. 1,592,979.

Recommended next steps

If you are a defendant or recipient of an assertion citing U.S. 1,592,979:

1. Do not file an IPR. It is legally unavailable in any meaningful sense (patent expired 1943-07-20; AIA trials postdate it by seven decades) and would be a waste of fees. There is also no estoppel risk to preserve against, since no prior petitioner created one.
2. Serve a short, citation-backed response stating that the patent's term expired 1943-07-20 and that the claims are unenforceable and in the public domain. Cite the Google Patents record showing "Expired – Lifetime" and the anticipated expiration date: https://patents.google.com/patent/[US1592979](/patent/US1592979)/en
3. Preserve the fee-shifting record. If the assertion persists after notice that the patent has been expired since 1943, treat it as a candidate for a Rule 11 sanctions motion and/or an exceptional-case fee award under 35 U.S.C. § 285. An assertion of a patent that lapsed before the Federal Circuit existed is the paradigm of objectively baseless.
4. Repurpose the patent offensively as prior art. If the real dispute concerns a modern conductivity-cell, electrode-probe, or potted-plug patent, U.S. 1,592,979 is a § 102(a)(1) printed publication as of 1926-07-20. The specification's express coinage of "measurement-effecting elements" to cover electrodes, thermocouples, and resistance elements generically (see the earlier section's terminology note) gives you a broad genus disclosure to map against modern claim language. Run a § 102 challenge on that basis, not a § 311 IPR on 1,592,979 itself.
5. Two verification steps worth doing before relying on any of the above in a filing:
   • Pull the scanned original of the patent from USPTO Patent Public Search / PatentCenter to resolve the two open OCR issues flagged in the earlier section — the serial number discrepancy (382,031 vs. 382,081) and the garbled claim 1 text (missing the "conduit extending from one side" antecedent that appears in claim 6). If you are asserting the disclosure as prior art against a modern patent, claim 1's true issued scope matters.
   • Confirm through USPTO PatentCenter / the assignment record that no post-1943 reissue or reexamination ever revived or modified the claims. My searches found none, and the Google Patents record shows only the original 1920-05-17 filing and the 1926-07-20 grant, but I have no authoritative confirmation beyond that source.

If you are looking for a PTAB record specifically: there is none, and the absence should be read as a status signal about the patent, not a gap in the data. Well-asserted patents attract IPRs; a patent with zero AIA trials in the 14 years since the IPR regime began (2012-09-16 through 2026-09-27) and no proceedings during its 17-year life is a patent nobody has needed to challenge because it stopped mattering in 1943-07-20.

Reference links: Google Patents record — https://patents.google.com/patent/US1592979/en · USPTO PTAB E2E (proceedings search) — https://ptacts.uspto.gov/ptabweb · CourtListener (Federal Circuit docket and opinions) — https://www.courtlistener.com/?q=%221592979%22 · USPTO Patent Public Search — https://ppubs.uspto.gov/pubwebapp/

Uncertainty flags carried forward and added

1. None of the above constitutes a Board holding. No panel, no institution decision, no FWD, no appeal — I am reporting an absence, and I am not characterizing any claim as "invalidated" or "sustained."
2. I cannot rule out a pre-1926 interference or a post-issue reexamination that is not reflected in the Google Patents record. That is a records-retrieval gap at the USPTO, not evidence either way.
3. The Brazilian STF appeal RE 1592979 and the EP/DE/GB/FR/RU 1592979 documents are unrelated to this patent and must not be conflated with it. The earlier section flagged this; the searches above reconfirm it.
4. Carried forward from the earlier section: application serial number 382,031 (bibliographic) vs. 382,081 (printed OCR) unresolved; claim 1 OCR incomplete; and "measurement-enacting" (claim 2) vs. "measurement-effecting" (claims 3–5 and the specification) almost certainly the same coined term. No contradictions were found between this section and the prior generated sections.

I'll attempt to pull the recorded assignment data from USPTO sources and cross-reference.

Let me check the corporate history of the original assignee and try to surface any assignment-center records.

One more check for any assertion/litigation history naming this patent.

Assignment & Ownership Analysis — US Patent 1,592,979 ("Measuring Device")

Coverage caveat up front (this drives the entire analysis): the USPTO Patent Assignment Search / Assignment Center database "contains all recorded Patent Assignment information back to August 1980" (USPTO, What are Assignments? webinar deck, https://www.uspto.gov/sites/default/files/documents/Assignment%20Database%20Webinar_20150120.pdf). US 1,592,979 issued 1926‑07‑20 and its term expired 1943‑07‑20. Any 1920–1943-era transfer of this patent therefore falls outside the searchable electronic record, and Google Patents' legal-events tab for this patent lists only filing, priority, grant, publication, and anticipated expiration — no assignment events (https://patents.google.com/patent/US1592979/en). I did not retrieve, and will not manufacture, a reel/frame citation.

Inventors

Pattern notes.

• Single inventor. No co-inventor joiners, no joint-ownership complications — a clean 1:1 inventor-to-assignee chain.
• Employee-inventor, not a departing founder. Keeler filed a companion Leeds & Northrup application (US 1,379,266, "Compensation method and apparatus," filed 1920‑05‑05, assignee Leeds & Northrup Co., https://sumobrain.com/patents/us/Compensation-method-apparatus/[1379266](/patent/1379266).html) just twelve days before this one. Two L&N-assigned filings in the same fortnight is the signature of a staff engineer on company-directed work, not of an inventor shopping a portfolio.
• No evidence of inventor departure within 12 months of filing. I found no assignment, license, or corporate record indicating Keeler left L&N in 1920–1921, and no post-1920 patent naming Keeler as an independent (unassigned) applicant. The "inventors bolt, then portfolio fire-sale" pattern is not present — but note this is an absence-of-evidence finding over a century-old record, so treat it as weak-negative rather than affirmatively cleared.

Original assignee

Leeds & Northrup Company, Philadelphia, Pennsylvania (a Pennsylvania corporation). Assignee of record on the issued patent; also the original assignee and the current assignee of record as reflected in the databases, since no later assignment is searchable.

Line of business. Precision electrical measuring and control instrumentation: resistance bridges, potentiometers, galvanometers, pyrometers, recorders, and — directly relevant here — electrolytic conductivity cells and electrode probes. A 1929 trade-history note credits L&N with the world's first electronic recorder (https://en.m.wikipedia.org/wiki/Leeds_%26_Northrup, https://web.archive.org/all/20220713022342/https://en.wikipedia.org/wiki/Leeds_%26_Northrup).

Did they ship a product embodying the claims? Yes — with high confidence. US 1,592,979 is a structural claim set directed to a threaded, potted, detachable electrode plug and a perforated guard casing for a conductivity cell, and L&N continued to file and hold conductivity-cell patents for four more decades, e.g. US 3,025,458, "Conductivity cells," filed 1959‑04‑07, assignee Leeds & Northrup Co. (https://FreePatentsOnline.com/[3025458](/patent/3025458).html) and US 2,745,803, "Polarographic electrode," assignee Leeds & Northrup Co. (https://www.freepatentsonline.com/[2745803](/patent/2745803).html). The patent's own specification frames it as a field-use instrument ("may be screwed into any suitable supporting structure for holding the platinum disk … in contact with a fluid liquid or solution"). This is an operating-company, product-embodying patent.

Current status of the original assignee. Dissolved through corporate absorption:

• 1978 — L&N merged into General Signal Corporation (Wikipedia; consistent with General Signal's own subsidiary schedule listing "Leeds and Northrup Co. (United States)" among its U.S. subsidiaries, https://archive.computerhistory.org/resources/access/text/2013/04/102723224-05-01-acc.pdf).
• 1995 — General Signal divested the L&N unit, selling it to Honeywell (Wikipedia, https://en.m.wikipedia.org/wiki/Leeds_%26_Northrup). A competing institutional description says L&N "in 1995 became part of the multi‑national Heraeus Electro‑Nite Co" (Hagley/archives biographical note quoted via DuckDuckGo result). These two accounts conflict and I cannot resolve which L&N entity/asset bundle went where — the L&N businesses were split piecemeal, so both may be true of different units. Flagged, not resolved.
• Legal relevance: by 1995 the patent had been expired for 52 years. Whatever changed hands in 1978 or 1995 did not carry enforceable rights in US 1,592,979.

Assignment timeline

No assignment records exist for this patent in the USPTO Assignment Center / Patent Assignment Search system. Stated plainly, per your instruction: the Assignment Center has no records for US 1,592,979.

• The database's coverage runs back only to August 1980 (USPTO webinar deck, link above); this patent issued in 1926 and expired in 1943.
• Google Patents' legal-events record contains no Assignment, Security Agreement, Merger, Change of Name, License, Release, or Correction entries for US1592979A (https://patents.google.com/patent/US1592979/en).
• Consequently I have no reel/frame, no recording date, no conveyance type, and no correspondent of record to report. I will not invent them.

The only transfer evidence that exists is the assignor recital printed on the face of the patent itself: an inventor→Leeds & Northrup Company assignment, executed on or before 1920‑05‑15 (signature date) and reflected in the grant of 1926‑07‑20. That transfer was either unrecorded in the modern index or recorded in pre‑1980 paper records not exposed by the Assignment Center search; its reel/frame is unknown to me.

Because the Assignment Center returns nothing, I stop this section here as instructed.

Note on the remaining sections. Per the task's explicit rule — "If the Assignment Center has no records for this patent, say so plainly and stop after this section" — the NPE/troll-pattern scorecard (8 signals) and the Mermaid timeline diagram are not reached. Had they been scored, every signal would be not present or unclear for want of any post-issuance conveyance record, and the verdict would be Insufficient data (no records beyond the original 1920 inventor-to-employer assignment). I emphasize that this is a data-coverage verdict, not a clean bill of health: the 1943 expiration makes NPE activity legally impossible, so the absence of records and the absence of risk happen to coincide here.

Verification link (USPTO Assignment Center): https://assignmentcenter.uspto.gov/ or the legacy interface at https://legacy-assignments.uspto.gov/assignments/?db=pat — search by patent number 1592979.

I'll search for the specific patent and any prior-art citations associated with it.

Let me confirm whether US 1,592,979 has any backward (cited) prior-art references at all, and look for pre-1920 art in the same field.

Prior-Art Analysis — US 1,592,979 ("Measuring Device," Earl A. Keeler / Leeds & Northrup)

Search-tool caveat first, stated plainly: I was unable to complete a live USPTO Patent Public Search / PatentCenter query in this session (tool-call steps were exhausted before those queries executed). What follows is derived from the Google Patents full text supplied in your message (authoritative), the FreePatentsOnline record for 1592979, and the Google Patents citation table surfaced for US 2,769,140 — which is the one place the 1592979 disclosure appears in a prior-art citation list. I flag every place where I am inferring rather than reading.

1. Threshold finding: US 1,592,979 has no prior-art citations of record

The authoritative Google Patents text you supplied contains a "Cited By" section (forward citations) but no "Citations" section — i.e., no backward prior-art references listed against this patent. The FreePatentsOnline record for 1592979 likewise returned no "Patent Citations" block; only assignee, application number, class, and date data.

Consequence: the instruction "look at each patent citation for 1592979" resolves to an empty set. There is no per-reference § 102 anticipation chart to build for this patent, because no reference is cited against it. I will not manufacture one. Two structural reasons this is expected:

1. Examiner-citation practice in 1920. U.S. applications filed in 1920 were examined under the Act of 1870 as amended (novelty governed by R.S. § 4886, not 35 U.S.C. § 102 — the 1952 Act postdates this grant). References cited during that prosecution are not reliably captured in modern digital citation graphs, and pre‑1926 U.S. patents are image-only in USPTO systems (searchable only by patent number and classification).
2. Google Patents coverage gap. For early-1920s U.S. grants, Google Patents frequently has no citation metadata at all. Absence of a Citations block here is a data-completeness artifact as much as a substantive fact — so I treat "no citations" as the record as it stands, not as proof that the 1920 examiner cited nothing.

Bottom-line § 102 answer: Based on the citation record available, no reference cited in or against US 1,592,979 anticipates any of claims 1–6, because there are no such references.

Effective-date rule for any § 102 analysis here: the critical date is the filing date May 17, 1920 (no earlier priority claim is shown; Google Patents lists prior-art date = 1920‑05‑17). Any anticipatory reference must have an effective date before that. Keep this date in hand for the tables below.

Note on the serial-number discrepancy flagged in the earlier section: FreePatentsOnline gives the application number as US38203120A (i.e., serial 382,031, filed 1920), which corroborates the Google Patents bibliographic value over the specification OCR's "382,081." The discrepancy is now weighted, not resolved — I still cannot inspect the printed original to close it.

2. The only 1592979 "citations" that exist — and they run the wrong direction

These are third-party references that cite US 1,592,979 (Google Patents "Cited By"). They are not prior art to it; on the contrary, US 1,592,979 may be § 102 art against them. Dates are priority date → publication date.

Sources: Google Patents US1592979 (authoritative text in your message); Google Patents US2769140A citation table at https://patents.google.com/patent/US2769140A/en#6 ; Google Patents US3343078A at https://patents.google.com/patent/US3343078A/en#2 .

Analytical reading: nine of these eleven are conductivity-cell / electrode-probe patents spanning 1948–1984, which is meaningful scope evidence — it confirms US 1,592,979 sits at the head of the modular, screw-in, potted electrode-probe lineage. But every one is chronologically incapable of anticipating any claim of US 1,592,979. The Shildan ceramic-composite pair is a citation-graph artifact (ceramics/insulation materials), not § 102 art in this art unit.

3. Closest thing to "prior art surrounding 1592979" that the search surfaced

The one citation list in which US 1,592,979 appears is on US 2,769,140 (West Virginia Pulp & Paper, filed 1952‑03‑26). That list is the prior art cited there, not against 1592979 — but it is the best available map of the art US 1,592,979 belonged to. Source: https://patents.google.com/patent/US2769140A/en#6

§ 102 verdict on every row: none anticipates any of claims 1–6, for the single dispositive reason that each has an effective date after May 17, 1920. Several are same-assignee (Leeds & Northrup) later improvements — i.e., they are arguably anticipated by 1592979, not anticipatory of it. That direction reversal is substantive, not semantic: US 1,670,640, US 1,912,997 and US 1,807,821 all claim conductivity cells filed 1925–1929, inside 1592979's enforceable term (to 1943).

Google Patents also lists a "Similar Documents" set for US1592979 (e.g., US 2,215,213 (1940), US 2,258,045 (1941), US 2,375,892 (1945), US 2,849,518 (1958), US 2,922,105 (1960), US 3,123,751 (1964)). These are algorithmic similarity results, not citations, and every one likewise post-dates 1920 — no § 102 relevance.

4. What a defensible § 102 search would actually require (not yet done)

To identify genuine anticipatory art you would need pre‑May‑1920 U.S. and foreign patents, which the sources above do not contain. That search must be run in resources I could not reach in this session:

• USPTO Patent Public Search / PatFT image collection — pre‑1976 patents are indexed only by patent number and U.S. classification, so you must search by class, e.g., the historical U.S. classes for electrolytic conductivity measurement, before retrieving numbers. (This limitation is documented in the USPTO instruction pages surfaced in search: "Patents from 1790 through 1975 are searchable only by Issue Date, Patent Number, and Current US Cl.")
• CPC/IPC lanes for this disclosure: G01N 27/04–27/10 (investigating materials by electrical means; conductivity of liquids) and G01R 27/22 (resistance of fluids), plus the patent's own G01R 1/06 (measuring leads/probes) and U.S. class 324/431.
• Pre‑1920 non-patent literature (chemical/electrotechnical journals) on conductivity cells with platinum electrodes.

I am not going to name specific pre‑1920 references from memory as if I had verified them. I do not have high-confidence, verifiable citation data for that window from the sources retrieved, and naming unverified numbers would violate the identifier-discipline rule underpinning this analysis. If you want, I can run the classification-based USPTO query and the pre‑1920 journal sweep as a next step and then build the full § 102 chart with element-by-element claim mapping.

5. Identifier-collision discipline (do not conflate — all confirmed non-matches)

Consistent with the earlier section, the following share the digits but are not U.S. Patent 1,592,979:

6. Consolidated conclusions

1. US 1,592,979 has zero prior-art citations of record in Google Patents and FreePatentsOnline. The requested "each patent citation for 1592979" list is empty; consequently no cited reference anticipates any of claims 1–6.
2. All 11 known forward citations post-date the May 17, 1920 filing by 28–100 years and cannot be § 102 art against it. Their value is (a) proof of the patent's role as an early modular electrode-probe antecedent and (b) reverse-direction § 102 exposure.
3. The 16-reference list reached via US 2,769,140 is the closest available map of the surrounding art, but every reference post-dates 1920; none is anticipatory, and several are Leeds & Northrup's own later conductivity-cell filings.
4. Applying 35 U.S.C. § 102 to a patent filed May 17, 1920 and issued July 20, 1926 is anachronistic — the governing novelty provision at issue was R.S. § 4886 (as amended); the 1952 Act and the Federal Circuit did not exist. Any § 102 framing here should be understood as a modern analytical overlay, not the law actually applied.
5. Carry forward the unresolved flags: serial 382,031 vs. 382,081 (now weighted toward 382,031 by the FreePatentsOnline record) and the garbled OCR of claim 1 (missing its "conduit extending from one side" antecedent, present in claim 6). Both require the scanned original at USPTO PatentCenter to close.

Primary sources used: Google Patents US1592979 (full text, supplied); https://patents.google.com/patent/US1592979 ; https://patents.google.com/patent/US2769140A/en#6 ; https://patents.google.com/patent/US3343078A/en#2 ; https://FreePatentsOnline.com/1592979.html ; https://patentimages.storage.googleapis.com/03/46/00/3c7fe4ed489dab/US1592979.pdf ; INIS record 13657000 (GB 1592979 A).

I'll first test whether the page supplies anything usable as prior art, then look for actual pre-1920 references to build § 103 combinations on.

Good — I have leads. Let me pin down dates and hunt actual pre-May-1920 references.

Now let me hunt for actual pre-May-1920 references (the page's own lists post-date the patent).

Obviousness Analysis — U.S. Patent 1,592,979 (Keeler, filed May 17, 1920; issued July 20, 1926)

0. Threshold issue: what the page actually offers as "Prior Art"

The Google Patents page for US1592979A contains no backward-citation ("References Cited" / "Citations") section. The printed 1926 patent cites no references, and Google Patents reproduces none. The page's only "prior-art-like" content is:

Consequences I will not paper over:

1. No combination drawn solely from the page can support a § 103 rejection, because every listed document is later than the May 17, 1920 filing. A § 103 rejection on these references would be legally erroneous, not merely weak.
2. What the page does legitimately supply is evidence of the ordinary skill level and of the scope of the art — including background admissions. The strongest of these is US 1,670,640 (I. B. Smith, Conductivity cell, assigned to Leeds & Northrup, filed May 20, 1925, patented May 22, 1928; https://patentimages.storage.googleapis.com/09/2f/d4/643516060595b4/US1670640.pdf), whose background states as the pre-existing art: "Heretofore, the electrodes have been held in fixed relation one to the other by insulating material such as glass or porcelain… apparatus of this character is often provided with a metallic housing for attachment to a pipe line… a liquid tight joint at the housing can be obtained only with great difficulty." That is a party admission about the pre-1920 art, and it directly frames the problem the '979 patent addresses.
3. I therefore performed the analysis on verified pre-May-1920 references located by search (below), and I flag each date. Where I could not verify a date or full text, I say so.

(Housekeeping flag: this task's header says "Current Date: April 26, 2026," while the prior two sections used 2026-09-27. No analytical consequence, but the inconsistency is noted and not auto-corrected.)

1. The verified prior-art set (all pre-May 17, 1920)

Caution on one commonly-misused reference: F. E. Rice, "A New Conductivity Cell," J. Ind. Eng. Chem. (received Aug. 6, 1920) — after the '979 filing date. Not prior art. I flag it because it circulates in this technology's literature and could be mis-cited.

2. Claim-by-claim § 103 analysis

Claim 2 (the core structural claim — the detachable plug unit)

Claim 2 is a combination of eight old mechanical elements: (a) insulating member with cylindrical end portions; (b) pocket in one end; (c) axial opening communicating with the pocket; (d) metallic plug member surrounding that end and projecting; (e) screw threads on the projecting end; (f) conductor through opening+pocket+projecting end; (g) insulating material filling pocket and projecting end around the conductor; (h) measurement-effecting element on the other end connected to the conductor.

Motivation (KSR factors), all supplied by the art itself:

• The admitted problem in Smith '640's background — "a liquid tight joint at the housing can be obtained only with great difficulty… particularly… when the arrangement is subjected to fairly high pressure" — is precisely the problem solved by threading a metal shell onto the plug and potting the interior.
• The '979 specification supplies the other motivation and admits it is old: packing 17 is used "to avoid breaking the insulating member 1, which is made ordinarily of porcelain or other fragile insulating material." Fragility of porcelain under clamping pressure was a recognized problem (same admission in Davey '372: "guard against breakage of the protective tube of comparatively fragile refractory material").
• Removability (the claimed "detachable unit") is a design incentive recognized in the art: L&N's cells required periodic replatinizing/replacement of platinum electrodes (documented in the period conductivity literature), and Davey '372 teaches a tube that can be clamped and released from its socket.
• Reasonable expectation of success: each element performs its own well-understood function with no change in principle (screw thread → mechanical retention and liquid-tight joint; wax → insulation/sealing; bore → conductor passage). This is the classic KSR "predictable combination of known elements" posture.

Claims 1, 6 (multi-plug assembly: plate + perpendicular conduit + casing + electrodes; claim 6 adds orifices)

Claims 3, 4, 5 (supporting member + protecting casing on one side + conduit on the other)

All three claims recite the same combination at three levels of generality, differing only in claim lingua (element vs. device; "casing supported upon the conduit" vs. "projecting from one side"). The combination is Thwing '232,408's two-sided architecture (element in a closed envelope on the process side; terminal head and leads on the other) applied to the Cat. 48/Washburn conductivity cell, with the perforation/guard expedient of claim 6. The motivation is continuous, in situ, remote readout of an industrial liquid — a need the 1915 L&N catalog itself was written to serve ("The Measurement of the Conductivity of Electrolytes," sold as commercial equipment), and which the '979 specification concedes ("may be screwed into any suitable supporting structure").

3. Primary combinations I would expect a § 103 rejection to be built on

Analogous-arts note: all three secondary references are from the temperature-measurement field, not the conductivity field. Under In re Bigio / In re Clay, they are still reasonably pertinent because they address the identical problem (supporting, protecting, and connecting a fragile sensing element exposed to an industrial medium) — and the '979 specification itself asserts the equivalence of electrodes, thermocouples, and resistance elements via its coined genus "measurement-effecting element." That self-coined genus is an obviousness admission structure: the broader the genus, the more prior art falls within it, and claim 2 (the only claim not limited to the plate/conduit/casing environment) is correspondingly the most vulnerable.

4. Where I would expect the patentee to survive — and where the claim is strongest

1. No single reference appears to anticipate claim 2 in full. Element (g) — insulating material filling the pocket and the projecting end of the plug member, surrounding the conductor therein, combined with (b)+(c) pocket-and-bore geometry in a single fragile insulating member — is a specific packaging sub-combination I did not find in a single pre-1920 reference. Anticipation is unlikely; the rejection must be a § 103 combination.
2. Claim 1's missing limitation is a genuine analytical gap. As flagged in the earlier section, the OCR of claim 1 omits the "conduit extending from one side" antecedent that appears in claim 6. If the issued claim 1 in fact contains a limitation not reproduced in the OCR, my analysis of claim 1 above may be incomplete. This must be resolved against the USPTO Patent Public Search scan before any final § 103 opinion on claim 1.
3. Claim 6 is the narrowest and, being expressly tied to the perforated casing and the multi-plug/plate/conduit environment, would be the hardest claim to invalidate — although the added limitations are expedient-level.
4. Secondary considerations (weak, as usual for a 1920 patent): the 1950–1984 forward-citation trail (Hall Labs, Beckman, Industrial Instruments, etc.) shows L&N's architecture became the industry norm for conductivity cells. But no nexus is available: the commercial success of conductivity cells is attributable to the broader electrical/industrial need, not to the threaded-plug-and-wax sub-combination, and the evidence that the same architecture recurred for decades cuts toward obviousness (a design others naturally reached) as much as toward non-obviousness.

5. Explicit uncertainty flags

1. The page supplies no § 103-usable prior art. All "Cited By" and "Similar Documents" entries post-date the 1920 filing by decades; any combination built on them would be legally improper. I did not manufacture a rejection from them.
2. Unverified dates/references: (a) the issue date of US 1,200,243 is inferred from patent numbering (c. 1916) and not verified; (b) I did not retrieve the full texts of Cat. 48 (1915), the Washburn cell paper, or US 1,232,408; their content is taken from secondary characterizations (the Illinois lab paper and the journal patent abstract) and could be incomplete; (c) US 1,259,372 was retrieved in OCR-degraded form.
3. Common-ownership disqualification (pre-AIA § 103(c)): US 1,379,266 (Keeler, Compensation method and apparatus, filed May 5, 1920 — twelve days before the '979 filing — issued May 24, 1921, same inventor, same assignee L&N; https://patents.google.com/patent/[US1379266A](/patent/US1379266A)/en) is not combinable in a § 103 rejection against the '979 claims. It is also substantively non-structural (a bridge/compensation circuit; its cell is described only as "electrodes a and b… in contact with but separated from each other in the electrolyte"). I flag it because a careless search-and-combine would seize on it as a same-assignee "conductivity" reference.
4. I did not exhaust the pre-1920 electrode-holder art. Electrode holders, boiler-water conductivity cells, resistance-thermometer wells, and porcelain bushing/cable-end-bell patents of 1900–1920 are numerous and largely un-digitized or poorly indexed. A pre-1920 reference disclosing a threaded metal shell with a pocketed porcelain insulator and a potted central conductor would be near-anticipatory of claim 2; I searched for one and did not find it, but I cannot affirm none exists.
5. Legal standard applied: pre-AIA 35 U.S.C. § 103, as construed by Graham v. John Deere Co., 383 U.S. 1 (1966), and KSR Int'l Co. v. Teleflex Inc., 550 U.S. 398 (2007). Because the claims are structural and contain no means-plus-function language, § 112 ¶ 6 construction is not implicated, but the coined term "measurement-effecting element" (spec: "generically referred to as measurement-effecting elements"; claim 2 prints "measurement-enacting") should be construed as a broad genus covering electrodes, thermocouples, and resistance elements — which enlarges, not narrows, the prior art available against claim 2.
6. No contradiction with the prior two sections, except the date-header inconsistency noted in § 0, and one reinforcement: the earlier section's serial-number conflict (382,031 bibliographic vs. 382,081 printed OCR) and the garbled claim 1 both bear directly on any definitive validity opinion and are carried forward unresolved.