SKETCH OF SIR WILLIAM THOMSON. 359 



" Consequently, there is a tendency in Nature for. all the energy in the uni- 

 verse, of whatever kind it be, gradually to assume the form of heat, and, having 

 done so, to become equally diffused. Now, were all the energy of the universe 

 converted into uniformly-diffused heat, it would cease to be available for pro- 

 ducing mechanical effect, since for that purpose we must have a hot source and 

 a cooler condenser. This gradual degradation of energy is perpetually going on ; 

 and sooner or later, unless there be some restorative power, of which we at 

 present have no knowledge whatever, the present state of things must come to 

 an end. 



"In 1854 Faraday, with an experimental cable, investigated the cause of the 

 retardation of signals first observed in the working of the cable between Har- 

 wich and the Hague. Thomson, taking up the question, published an investiga- 

 tion of the nature of the phenomenon, one practical result of which was that 

 with cables similar in lateral dimensions the retardations are proportional to 

 the squares of the lengths. This law is now commonly referred to as the ' law of 

 squares.' About this time it was proposed to construct a cable to connect Eng- 

 land with America ; and it became obvious that the discovery of the retardation 

 of signals raised a question whether the transatlantic cable would not prove a 

 commercial failure. Whitehouse, experimenting with 1,125 miles of cable, 

 found the transmission of an instantaneous signal to the farther end of the 

 cable to occupy one second and a half. The length of a cable required to con- 

 nect Ireland with Newfoundland is twice that of the experimental cable of 

 "Whitehouse; and thus, according to the law of squares, the time taken to trans- 

 mit an instantaneous signal through a cable similar in lateral dimensions to 

 that of Whitehouse, and joining those two places, would be no less than six sec- 

 onds. In 1856 Whitehouse read a paper before the British Association, in which 

 he described experiments by which he hoped to disprove the law of squares. 

 Thomson replied in the Athenceum (November 1, 1856); and subsequent experi- 

 ments have established the correctness of his law. 



"Fortunately a true understanding of the nature of the phenomenon of re- 

 tardation led Prof. Thomson to the method of overcoming the difficulties pre- 

 sented. The disturbance produced at the extremity of a long submarine cable 

 by the application for an instant of electromotive force at the other end is not, 

 as in the case of a signal through an overhead land-line, a pulse, practically in- 

 finitely short, and received only a minute fraction of a second after it was com- 

 municated. Instead of this, a long wave is observed at the farther extremity, 

 gradually swelling in intensity, and as gradually dying away. Its duration for 

 such a cable as we have been speaking of would be the whole six seconds, cal- 

 culated from the experiments of Whitehouse. Prof. Thomson perceived that an 

 instrument was required which should give an indication of a signal received 

 long before the wave has acquired its maximum intensity, and in which the sub- 

 sequent rising to maximum intensity should not render unreadable a fresh signal 

 sent quickly after the previous one. This was effected by his ' mirror galva- 

 nometer ; ' and it was by means of it that the messages transmitted through the 

 1858 Atlantic cable were read. 



" The 1858 cable, submerged under difficulties that many times threatened to 

 be insurmountable, soon failed. Several important messages were, however, 

 transmitted through it ; and it served to prove the feasibility of the project 

 which many eminent engineers up till that time regarded as chimerical. Before 

 another attempt was made tbe labors of Prof. Thomson and others,, to all of 

 whom the world owes a deep debt of gratitude, had so improved the construe- 



