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VII. On the Atmosphere as a Vehicle of Sound. 
By John Tyndall, B.C.L . , LL.D., F.B.S. 
Received February 5, — Read February 12, 1874*. 
§ 1. Introduction. 
The cloud produced by the puff of a locomotive can quench the rays of the noonday 
sun; it is not therefore surprising that in dense fogs our most powerful coast-lights, 
including even the electric light, should become useless to the mariner. 
Disastrous shipwrecks are the consequence. During the last ten years no less than 
two hundred and seventy-three vessels have been reported as totally lost on our own 
coasts in fog or thick weather. The loss, I believe, has been far greater on the American 
seaboard, where trade is more eager and fogs more frequent than they are here. No 
wonder, then, that earnest efforts should have been made to find a substitute for light in 
sound-signals, powerful enough to give warning and guidance to mariners while still at 
a safe distance from the shore. 
Such signals have been established to some extent upon our own coasts, and to a still 
greater extent along the coasts of Canada and the United States. But the evidence as 
to their value and performance is of the most conflicting character, and no investigation 
sufficiently thorough to clear up the uncertainty has hitherto been made. In fact, while 
the velocity of sound has formed the subject of refined and repeated experiment by 
the ablest philosophers, since the publication of Dr. Derham’s celebrated paper in the 
Philosophical Transactions for 1708, no systematic inquiry has, to my knowledge, been 
made into the causes which affect the intensity of sound in the atmosphere. 
As an attempt to fill the blank here indicated, I beg to submit to the Boyal Society 
some account of an investigation on fog-signals recently carried out at the instance of, 
and in conjunction with, the Elder Brethren of the Trinity House. Soon after my return 
from America I was requested, as the scientific adviser to the Corporation, to undertake 
the direction of this inquiry. I entered upon it inspired by duty rather than hope, 
for I feared that the observations would be tedious and the scientific results uncertain. 
But the study of any natural problem, if only steadfastly pursued, is sure in the end to 
reward the inquirer. And so in the present instance, after some preliminary groping, 
* These dates apply to the chief points of the paper in its complete state, including the experiments on mix- 
tures of gases and vapours and on differently heated air. A copious preliminary account, embracing the obser- 
vations made at sea and the conclusions founded thereon, was read on January 15 (Proceedings, vol. xxii. p. 58). 
The experiments on the effect of fumes, &c. (§ 13) were described before the Society on May 21. In rearranging 
the paper with the view of throwing certain details into an appendix, these last experiments have been, 
embodied in the original paper. 
