EDITOR'S TABLE. 



753 



the views which have generally pre- 

 vailed 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 1S73. This peri- 

 od he characterizes as a Hank. 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 "ig- 

 noring " 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 arti- 

 cle 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 ser- 

 vice of the United States, and must there- 

 fore be of interest to our distinguished vis- 

 itor. 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. 



vol. ix. 48 



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 

 wavi's of sound, like those of light, are ab- 

 sorb 1 or stifled by fog ; on this point, how- 

 evei observers disagree. At first sight, 

 fron 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 di- 

 rected 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 men- 

 tioned estimate their distance with consid- 

 erable precision by the number of revolu- 

 tions 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 pene- 

 trating power of sound, or, in other words, 

 produce an effect analogous to the propaga- 

 tion 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 analo- 

 gy 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 dimi- 

 nution 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 compari- 

 son with another cause, vis., that of the influ- 

 ence of wind. During a residence of several 

 weeks at the sea-shore, the sound of the 

 breakers at a distance of about a mile in no 



