Page:Popular Science Monthly Volume 9.djvu/781

Rh the views which have generally prevailed upon the subject since, "marks the latest systematic inquiry into the causes which affect the intensity of sound in the atmosphere," up to the time of his own investigations in 1873. This period he characterizes as a blank. He does not deny that facts of importance had been observed in the interval, or that partial inquiries had been made leading to valuable conclusions; but the "blank" is declared to consist in the absence of any "systematic inquiry into causes," such, of course, as generally lead, when ably conducted, to the reconciliation of conflicting views, and the establishment of principles which are entitled to take their place in the body of scientific knowledge. To this the writer in the Nation replied that Prof. Henry had made such systematic inquiries, and that Prof. Tyndall knew it from a paper which he heard Prof. Henry read in Washington. The evidence of the charges against Prof. Tyndall of "ignoring" or "suppressing" the work of Henry, or of taking advantage of it in his own subsequent investigation, is, therefore, to be found in this paper, if anywhere. The writer of the article in the Nation did not adduce the article, although his whole case rested upon it. Challenged for his evidence, he now brings it forward in the Tribune, makes extracts from it, and states what else it contained; and we now give his whole reference to it, italics and all:

"Prof. Henry prefaced his paper on that occasion with the following reference to Dr. Tyndall' s presence: 'The communication which I propose to make this evening is brought forward at this time especially on account of the presence of Dr. Tyndall, he being connected with the lighthouse system of Great Britain, while the facts I have to state are connected with the lighthouse service of the United States, and must therefore be of interest to our distinguished visitor. The facts I have to present form part of a general report to be published by the United States Lighthouse Board.'

"After briefly treating on the prevalence of fogs upon the American coast, Prof. Henry proceeded to consider their scientific relations to fog-signaling, and remarked as follows:

"'In studying this subject it becomes a question of importance to ascertain whether waves of sound, like those of light, are absorbed or stifled by fog; on this point, however observers disagree. At first sight, from the very striking analogy which exists in many respects between light and sound, the opinion has largely prevailed that sound is impeded by fog. But those who have not been influenced by this analogy have in some instances adopted the opposite opinion that sound is better heard during a fog than in clear weather. To settle this question definitely the Lighthouse Board have directed that at two lighthouses on the route from Boston to St. Johns the fog-signals shall be sounded every day on which the steamboats from these ports pass the station, both in clear and foggy weather, the pilots on board these vessels having, for a small gratuity, engaged to note the actual distance of the boat when the sound is first heard on approaching the signal, and is last heard on receding from it. The boats above mentioned estimate their distance with considerable precision by the number of revolutions of the paddle-wheel, as recorded by the indicator of the engine, and it is hoped by this means to definitely decide the point in question. We think it highly probable that fog does somewhat diminish the penetrating power of sound, or, in other words, produce an effect analogous to the propagation of light. But when we consider the extreme minuteness of the particles of water constituting the fog, as compared with the magnitude of the waves of sound, the analogy does not hold except in so small a degree as to be of no practical importance, or, in other words, the existence of fog is a true, but, we think, an insufficient, cause of diminution of sound, which view is borne out by the great distance at which our signals are heard during a dense fog. Another cause, which without doubt is a true one, of the diminution of the penetrating power of sound is the varying density of the atmosphere, from heat and moisture, in long distances. The effect of this, however, would apparently be to slightly distort the wave of sound rather than to obliterate it. However this may be, we think, from all the observations we have made, the effect is small in comparison with another cause, vis., that of the influence of During a residence of several weeks at the sea-shore, the sound of the breakers at a distance of about a mile in no