In 1866 Jenkin was appointed to the professorship of Engineering in University College, London. Two years later his prospects suddenly improved; the partnership began to pay, and he was selected to fill the Chair of Engineering, which had been newly established, in Edinburgh University. What he thought of the change may be gathered from a letter to his wife: 'With you in the garden (at Claygate), with Austin in the coach-house, with pretty songs in the little low white room, with the moonlight in the dear room upstairs--ah! it was perfect; but the long walk, wondering, pondering, fearing, scheming, and the dusty jolting railway, and the horrid fusty office, with its endless disappointments, they are well gone. It is well enough to fight, and scheme, and bustle about in the eager crowd here (in London) for awhile now and then; but not for a lifetime. What I have now is just perfect. Study for winter, action for summer, lovely country for recreation, a pleasant town for talk.' The liberality of the Scotch universities allowed him to continue his private enterprises, and the summer holiday was long enough to make a trip round the globe. The following June he was on board the Great Eastern while she laid the French Atlantic cable from Brest to St. Pierre. Among his shipmates were Sir William Thomson, Sir James Anderson, C. F. Varley, Mr. Latimer Clark, and Willoughby Smith. Jenkin's sketches of Clark and Varley are particularly happy. At St. Pierre, where they arrived in a fog, which lifted to show their consort, the William Cory, straight ahead, and the Gulnare signalling a welcome, Jenkin made the curious observation that the whole island was electrified by the battery at the telegraph station. Jenkin's position at Edinburgh led to a partnership in cable work with Sir William Thomson, for whom he always had a love and admiration. Jenkin's clear, practical, and business-like abilities were doubtless an advantage to Sir William, relieving him of routine, and sparing his great abilities for higher work. In 1870 the siphon recorder, for tracing a cablegram in ink, instead of merely flashing it by the moving ray of the mirror galvanometer, was introduced on long cables, and became a source of profit to Jenkin and Varley as well as to Sir William, its inventor. In 1873 Thomson and Jenkin were engineers for the Western and Brazilian cable. It was manufactured by Messrs. Hooper & Co., of Millwall, and the wire was coated with india-rubber, then a new insulator. The Hooper left Plymouth in June, and after touching at Madeira, where Sir William was up 'sounding with his special toy' (the pianoforte wire) 'at half-past three in the morning,' they reached Pernambuco by the beginning of August, and laid a cable to Para.