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William Thomson, Lord Kelvin 1824-1907

A web exhibition of manuscripts from the collections
of the University of Glasgow Library
Originally exhibited in 1977; adapted for the web in 2008


Introduction | Boole | Joule | Maxwell | Atlantic Cable | Jenkin | Varley | Tait | Darwin | Other correspondents | Miscellany


A devoted electrician, Varley studied telegraphy after leaving school and then worked for 18 years for the Electric and International Co. until the telegraphs were acquired by the Government in 1868. Retiring to a private life, he focused his energies on making electrical inventions, including a precursor of the telephone.

Of Varley's capacities as an electrical engineer Thomson was in no doubt. In a letter to the Secretary of the Atlantic Telegraph Co. of 24 September 1858, when Varley had reported on the fault in the Atlantic cable and Thomson was still hopeful that the cable could be saved, he wrote that "Varley's report is, in my opinion, evidence of high scientific and practical talent". Thomson nominated him for membership of the Electrical Standards Committee of the British Association - others were Clerk Maxwell and Joule - which in 1864 determined the standard of resistance, the ‘B.A. unit’ or ‘ohmad’, since shortened to ‘ohm’.

To the work on the Atlantic cable Varley made a highly important contribution, first in finding a method of localising faults in submarine cables, and then in devising an ‘artificial cable’, making it possible to study in the laboratory the way cables would react in working conditions. He also invented the use of the signalling condenser to sharpen electric pulses transmitted through a cable, so increasing the speed of working.

The Atlantic cable and other telegraphic work, including protracted negotiations over fees and patent rights, form the basis of the correspondence between Varley and Thomson in the Kelvin Papers, which consists of some forty letters written between 1859 and 1869.


To read the selection of letters in full, click on the thumbnails to view larger versions & then click on the 'back' button to return to this page (depending upon your browser, in viewing the larger version, you may have to click upon an additional button which will appear at the lower right corner to see the image at its largest size)


10 October 1859 (MS Kelvin V2)

"... In answer to your question about testing by means of positive and negative currents to ascertain the distance of a fault in a cable, I first used this means... [on] our Dutch cables in August 1853… I began practical telegraphing in 1847 and noticed the same year the difference produced by positive and negative currents and recommended all testing to be performed with negative currents or both negative and positive..."


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9 January 1860 (MS Kelvin V3)

"... I have very recently tested the speed of the electric wave in a novel manner and demonstrated experimentally that your law of squares [i.e. that the retardation of an electrical impulse sent through a cable of a given type of construction is proportional to the square of the distance] is correct…"


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27 November 1865 (MS Kelvin V11)

"… I had proposed that we should have a new name for every thousand units. Jenkin objects... and one objection is a good one (and will apply to me and to you) viz: he writes so badly that if the magnitude be expressed by a termination, Ohmad [1 unit] and Ohmon [1 million units] will be confounded by indistinct writing.."


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15 January 1866 (MS Kelvin V13)

"Specification of Messrs Thomson and Varley for improvements in electric telegraphs."


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10 June 1868, to Sir Richard Glass, Chairman of the Atlantic Telegraph Co. (MS Kelvin V20)

"... You requested me to state concisely in what respects the Atlantic enterprise has been and is benefited by the inventions and labours of Thomson, Jenkin and myself..."


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12 November 1868 (MS Kelvin V27)

"... The ... electric balance for which the world is mainly indebted to you was and is excellent. I will call it the Thomson Balance. Now I am going to propose another which I am having made and which I shall call the Varley Balance..."


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Go to next section: correspondence with Peter Guthrie Tait

Go to next section: correspondence with Cromwell Fleetwood Varley