754 



THE POPULAR SCIENCE MONTHLY 



case appeared to be coincident with the va- 

 riations of an aneroid barometer or a ther- 

 mometer, but in every instance it was affect- 

 ed by the direction of the wind. The va- 

 riation in the distinctness of the sound of a 

 distant instrument as depending on the di- 

 rection of the wind is so marked that we are 

 warranted in considering it the principal 

 cause of the inefficiency in certain cases of the 

 most powerful fog-signals,'' 



"In the remainder of his paper, as read 

 in the presence of Prof. Tyndall, the chair- 

 man of the Lighthouse Board applied the 

 hypothesis of Prof. Stokes to an explanation 

 of certain abnormal phenomena of sound 

 which had been observed during the course 

 of his systematic inquiries with regard to 

 the causes which affect the intensity of 

 sound." 



The reader now has the whole case 

 before him. This is the substance of 

 what Prof. Tyndall listened to in Wash- 

 ington, and for not recognizing which, 

 to the credit of American science, in his 

 book on sound, he has been the subject 

 of a bitter and persistent newspaper 

 attack. Prof. Tyndall says that the 

 reading of the document left him in 

 mental perplexity, and we are certainly 

 not surprised at his state of mind. The 

 subject, it is to be remembered, was not 

 new to him. He had been for years 

 engaged in the scientific service of the 

 English Lighthouse Department; he 

 had been an explorer in the field of 

 acoustics, and was familiar with the 

 history of the subject. He knew that 

 it was involved in obscurity, that ob- 

 servations disagreed, and that there was 

 much theoretical conflict about it. Noth- 

 ing seemed established, and he states 

 that Prof. Henry's paper left him still 

 in an intellectual fog in regard to the 

 whole question. The reader will see 

 that the statement is pervaded by doubt. 

 Conflicting opinions are given, and the 

 prominent question was yet to be de- 

 cided by the aid of Boston pilots. Fi- 

 nally, a conjecture, thrown out by an 

 English physicist, is invoked for the ex- 

 planation of anomalous effects observed. 

 Clearly it was a case for further and for- 

 midable work which required to be met 



by a comprehensive, systematic, and 

 thorough-going research. Prof. Hen- 

 ry's paper settled nothing. That it 

 was without value as a contribution to 

 science, we by no means assert; but 

 every one can see that it was not the 

 product of a full, methodical, and ex- 

 haustive inquiry, such as the subject 

 urgently demanded and had not yet re- 

 ceived from any source. The observa- 

 tions of Humboldt, early in the cen- 

 tury, on the passage of sound, were im- 

 portant, as Prof. Tyndall himself attests, 

 but to characterize them as a " system- 

 atic inquiry into the causes which af- 

 fect the intensity of sound in the 

 atmosphere" is simply absurd. Hum- 

 boldt confined himself to one branch 

 of the investigation, and whole tracts 

 of it he did not touch. 



Prof. Tyndall was, therefore, abun- 

 dantly justified in assuming that the 

 blank of 167 years had not been 

 filled up ; and, being deeply interested 

 in the subject, and having command of 

 the means for an elaborate course of 

 researches upon it, he determined to 

 enter fully into the inquiry, with the 

 hope of dispelling some of the uncer- 

 tainty which clouded it. 



He took up the question from a pure- 

 ly scientific point of view, not to im- 

 prove the art of fog-signaling or arrive 

 at any immediate practical results valu- 

 able to the navigator, but simply to test 

 theories, explain phenomena, harmo- 

 nize discrepancies, and advance acous- 

 tical science. He attacked the problem 

 of the "causes" which affect the in- 

 tensity of sound in the air with a sin- 

 gle-mindedness, a rigor of method, and 

 a completeness of resources, that had 

 never before been employed upon it. 

 His researches went on in a double 

 series, on the coast and in the labora- 

 tory. Using the facilities furnished by 

 the Government at home, and sending 

 abroad for the best that could be sup- 

 plied, he carried on his observations and 

 experiments on a large scale from the 

 South Foreland Station, scrutinizing 



