It was the chief desire of him who has gone to the grave, that the link which unites England and America might bind the countries that he loved the most in indissoluble union. Though the two nations dwell apart, on opposite shores of the same great and wide sea, they are now brought almost within the sound of each other's voice and the touch of each other's hand: they can look into each other's eyes, and exchange their morning and evening congratulations with the rising and setting of each day's sun. May the instrument through which they look and speak never startle them with rude alarms, but continue to whisper peace in tones as gentle as the murmur of the sea, as long as the winds blow and the waters roll.
FOOTNOTES:
[A] The Berkshire Hills, Stockbridge, Massachusetts.
APPENDIX.
INSTRUMENTS FOR SIGNALLING ACROSS THE ATLANTIC OCEAN.
If the project of an Atlantic Telegraph be justly ascribed to the daring of an American, and its success to his courage and perseverance through years of struggle and disappointment; the solution of the scientific problem involved in it, is due to the genius of a Scotchman, whom the writer of this volume first knew (and it is a pleasant memory to have known such a man in the beginning of his splendid career) as Professor Thomson of the University of Glasgow, where his father had been professor before him, whom the son succeeded in the Department of Physics, which included the then little known science of Electricity, to which the young professor devoted himself with all the eagerness of scientific genius. The project of a telegraph across the ocean suggested new problems and new difficulties, to which he applied himself with characteristic ardor, the result of which is here given. When the second expedition of the Great Eastern (in 1866) was successful, the British Government at once recognized his eminent services; and the name of Sir William Thomson has since been recognized, among the leaders in scientific discovery, not only in England but all over the scientific world. The government has recently added a further dignity in making him a peer of the realm, an honor hitherto reserved generally for the leaders of armies, like Wellington. To confer it on a simple professor shows an advance of civilization in the respect paid to intellectual greatness. In conferring such a title, the government does not honor the man more than it honors itself. It is to the glory of England that such an honor should be paid to science in the person of Lord Kelvin, as was paid to literature in the person of Lord Tennyson.
The following, taken in substance from an English scientific review, will indicate briefly, but with sufficient clearness, the problem to be solved in signalling to great distances under the sea, and the instruments by which this is accomplished:—
The speed of signalling through a submarine cable depends upon its electrostatic capacity, which, unless it be very small, gives rise to "retardation."
In the Proceedings of the Royal Society for 1855, Sir William Thomson showed how the effect at the distant end of a cable, caused by the application of a battery at one end, could be calculated and represented graphically in what is called the "curve of arrival." After contact is first made at the sending end between the cable and one pole of the battery (the other pole being to earth), a certain interval of time elapses before any effect is felt at the distant end. This interval of time is denoted by the letter a. After the interval of time a has passed, a current begins to issue from the cable at the receiving end, and increases in strength very rapidly. After a further interval of 4a or after a period of 5a from the first application of the battery, it attains about half its maximum strength, and there is very little sensible increase in strength after a time equal to 10a has elapsed. The curve of arrival is drawn by taking distances along o x to represent intervals of time, and distances along o y to represent strengths of current. Curve No. I. shows the gradual increase in strength of the received current at one end of a cable when the battery is applied to and kept in contact with the other end. For a distance corresponding to the interval of time a, the curve does not sensibly deviate from the straight line o x; in other words, no effect is observable at the receiving end during this time.