1804 __ Pasley’s improvement of the telegraph
‣ Comment : First Lt. Pasley, as he then was, began work on telegraphs while stationed in Malta. He planned to make communication more rapid by transmitting four symbols at a time, instead of only one. In the Chappe system, the more than 200 possible positions of the arms were individually interpreted by means of a code book at terminals. The telegraph operators had no idea of the information they were transmitting, which was very agreeable to the totalitarian French. In Britain, however, the semaphore was interpreted as giving numbers that referred to letters, numbers, entries in a dictionary, or some such. The modern practice of spelling out messages as used with the electromagnetic telegraph was considered too time-consuming. Col. Pasley's polygrammatic telegraph with four sets of two arms arranged side-by-side was devised in Malta in 1804. When he passed through England in 1807, he modified the telegraph to use a single vertical post on which the four pairs of arms were pivoted, one above the other. This invention was published in Tilloch's Philosophical Magazine, v. 29, p. 292 (1807). (J. B. Calvert) — In 1822 Popham’s design was revised by Colonel (later General) Charles W. Pasley (1780–1861). The new system still had two movable arms, but this time each arm could be set in one of eight positions, producing 8×8 or 64 code combinations, and of course resembling the Depillon system even closer. The upper arm in Pasley’s design had a fixed V-shape, to make it easier to distinguish it. Pasley’s telegraph was used to reconstruct, for instance, the line from London to Portsmouth, which had been abandoned in 1816. The new line from London to Portsmouth was in operation from 1822 until 1847. A start was also made with the reconstruction of the branch to Plymouth, this time starting not at Beacon Hill but at a station called Chatley Heath, close to London on the new London to Portsmouth line. Construction on the branch to Plymouth started in 1825, but it was suspended in 1831 and never resumed. The use of the Pasley system, however, survived much longer still on ships. Its use, for instance, was reported during a review of the fleet at Spithead by Queen Victoria prior to its departure to the Crimean War in 1859. (Gerald J. Holzmann)
‣ Source : Calvert, James B. (rev. 2009), “The Origin of the Railway Semaphore : Its evolution from the optical telegraph”, University of Denver.
‣ Source : Gerard J. Holzmann, “The Use of Optical Telegraphs in England and Elsewhere”
‣ Urls : http://mysite.du.edu/~jcalvert/railway/semaphor/semhist.htm (last visited ) http://spinroot.com/gerard/pdf/optische95.pdf (last visited )
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