114 



THE POPULAR SCIENCE MONTHLY, 



EDITOR'S TABLE. 



THE PROTOPHONE IN RESEARCH. 



THE elegant research of Professor 

 Tyndall, which we publish in the 

 present number,will well repay the care- 

 ful attention of our readers. It is of in- 

 terest, not only on account of the very 

 complete confirmation of results pre- 

 viously obtained bj this physicist, but 

 also on account of the novel method 

 employed, and the promise this gives 

 of wide utility. The photophone is 

 barely six months old, but these experi- 

 ments show that it already has a large 

 field of usefulness before it, and it is, 

 perhaps, not too much to expect that it 

 will prove to be one of the most deli- 

 cate instruments at the command of the 

 physicist. The experiments are further 

 interesting for the very conclusive dem- 

 onstration they afford of the causes to 

 which the action of the instrument is 

 due. From the first, Professor Tyndall 

 states, he was convinced that the sounds 

 given out by bodies upon which the in- 

 termittent beam of light impinged were 

 due to their expansion and contraction 

 tinder the influence of radiant heat, and 

 this opinion is most fully borne out bj 

 the results obtained. The experiments, 

 while showing the great delicacy of this 

 beautiful instrument of Professor Bell, 

 also incidentally show that some of the 

 expectations with regard to it are un- 

 founded. One of these is, that with it 

 sounds upon the sun may be heard. 

 The fallacy of this has been recently 

 pointed out, and the arrangement of the 

 apparatus adopted by Professor Tyndall 

 clearly exhibits it. It consists in as- 

 suming that the sound given out by the 

 absorptive body is the reproduction of 

 a previous sound, while in reality all 

 that is necessary is that the impinging 

 beam be intermittent its variations 

 may be produced in any manner what- 

 ever. 



Of the results of previous experi- 

 ments confirmed by this later research, 

 the most important are those regarding 

 the behavior of dry air and the vapor of 

 water toward radiant heat. By a long 

 series of beautiful and refined experi- 

 ments. Professor Tyndall had shown that 

 the former was perfectly transparent to 

 such heat, while water-vapor was a 

 powerful absorbent of it. These results 

 have been disputed by other experiment- 

 ers, and it needed, to definitely settle the 

 controversy, some more delicate method 

 of testing these substances than that 

 furnished by the instruments heretofore 

 at command. This has been supplied 

 by this latest acquisition of science, and 

 the first use of it appears to fully sus- 

 tain Professor Tyndall's position. 



BOOK PHYSIOLOGY ABROAD. 



We often hear subdued expressions 

 of doubt as to the quality of the phys- 

 iological teaching prevalent in girls' 

 schools. It is intimated that the knowl- 

 edge the pupils get upon this subject is 

 generally of a very loose and vague 

 sort, so as to be but of little practical 

 use. It is objected to what girls learn 

 about in their physiological studies, that 

 it is not entitled to be called knowl- 

 edge at all that is, they do not really 

 IcnoiD what they are studying about, but 

 only remember certain statements as 

 well as they can, while the information 

 they get is not of a kind fit to be used. 

 Whatever may be the fact in regard to 

 our own schools, it is pretty certain 

 that the physiology taught to girls in 

 some of the English schools is marked 

 with all the bad qualities sometimes as- 

 cribed to our own. 



The London " Globe " gives a ludi- 

 crous illustration of the results of phys- 



