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CPRR Telegraph Key
CPRR Telegraph Key
CPRR Brooks Patent Aug. 6, 1867 Insulator for the Transcontinental Telegraph Line.

“Improvement in Insulators for Telegraph-Wires.”

The first transcontinental telegraph line of 1861 that ended the Pony Express (authorized by the Pacific Telegraph Act of 1860) was soon replaced by the multiwire telegraph line along the transcontinental railroad right of way.  The telegraph lines are visible in many of the railroad stereographs.  This railroad telegraph insulator, used in Utah, was manufactured for the Central Pacific Railroad using David Brooks patented design.  The round top of the insulator locks into a hole in the underside of the crossbar atop the telegraph pole, using the spike on the top front of the insulator to hold it in place.  A glass insulator inside the cast iron shell insulates the casing from the double hook that protrudes below to hold the telegraph wire.

    Brooks Insulator, top viewTop of the cast iron insulator.

    David Brooks' four patents Adobe Acrobat PDF format were dated: 
    November 29, 1864 (#45,221)
    March 26, 1867 (#63,206);
    August 6, 1867 (reissue, #2,717); and, 
    October 8, 1867 (#69,622 - showing the actual design used).

    [Also see Bill Meier's extensive insulator patent library.]

    Brook's Patent telegraph insulator as used on the Central Pacific Railroad in the 1860s.  Correct in every detail.  Gray metal cylinder measuring 6 1/8" long x 2" diameter, with a flat base upon which appears in raised cast letters 

    AUG 6 1867. 
    Opposite end is hollowed to receive a glass sleeve and a protruding cast metal wire hook, both of which are present as manufactured.  Undamaged and showing only normal aging.  This insulator was retrieved from the Utah desert north of the Great Salt Lake and west of the storied Promontory Summit.  This is the real thing, and an incredibly scarce transcontinental railroad artifact.
    Description Courtesy Paul Hedren.

    The Brooks Insulator (Fig 37) consists of a suspension hook cemented into an inverted blown glass bottle, which is again cemented into a cast iron shell, designed for attachment to a cross-arm, as in Fig. 38. The remarkable insulating properties of this arrangement are mostly due to the use of paraffine, with which the cementing material (sulphur) is saturated. It has also been discovered that blown glass possesses extraordinary properties of repelling moisture.
    Brooks Insulator PhotoBrooks Insulator Cross SectionBrooks Insulator, side view in cross-arm
    Engravings courtesy Charles Keith.

    Brooks Insulator, back viewSide view of the back of the insulator showing the double hook for the telegraph wire extending beneath the internal glass spacer.


    Transcontinental Telegraph

    History of Telegraphy

    Telegraph insulator timeline, including patent dates and numbers

    "Modern Practice of the Electric Telegraph," by Frank L. Pope.  New York, D. Van Nostrand, 1872.
    Courtesy Bill Meier.

    Glass Insulators

    19th Century Telegraph and the Railroads

    Insulator Picture Gallery - Ramshorn Style - Photo of Brooks Insulator Paraffin Wax Seal, in Crossarm

    Directory of Insulator Collecting Websites

    Neal McEwen's - Telegraph Keys

    The Telegrapher - History and Links

    The Life of a Telegraph Operator on the "Old C. P." in the Golden Spike Era

    Western Union Collection

    Telegraph Museum

    The Telegraph of To-day.  by Charles L. Buckingham, Scribner's Magazine, VI(1), p. 3, July, 1889

    Samuel F. B. Morse Papers at the Library of Congress

    Samuel Morse Historic Site

    Morsum Magnificat: The Morse Magazine

    Insulator Emporium and Insulator Price Guide

    The Sparks Telegraph Key Review

    E.C&M Co S.F. CPRR glass telegraph insulator, c. 1875


    Michael Bliss of Fort Collins, Colorodo notes that glass U.P.R.R./Mulford & Biddle; Chester; and S.O.E.X insulators were used across eastern Utah and through Wyoming to Nebraska on the Union Pacific Railroad.

    Lawrence K. Hersh notes that the Brooks insulators were replaced by Brookfield insulators, 1877 (Patent D9,858).

    One Brooks insulator has been reported to have been found in an SPRR tunnel in Oregon.

    One of these insulators was recently polished, giving the metal case and hook the appearance off polished brass rather than cast iron.



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