332 



THE POPULAR SCIENCE MONTHLY, 



that are exjyosed to the beam, and that the sounds are in every case due 

 to those rays of the spectrum that are absorbed by the body. 



The Spectrophoxe. Our experi- 

 ments upon the range of audibility of 

 different substances in the spectrum 

 have led us to the construction of a 

 new instrument for use in spectrum 

 analysis, Avhich was described and ex- 

 hibited to the Philosophical Society of 

 Washington last Saturday.* The eye- 

 piece of a spectroscope is removed, and 

 sensitive substances are placed in the 

 focal point of the instrument behind 

 an opaque diaphragm containing a slit. 

 These substances are put in communi- 

 cation with the ear by means of a hear- 

 ing-tube, and thus the instrument is con- 

 verted into a verita- 



5) 



ble " s2:)ectrophone, 

 like that shown in 

 Fig. 13. 



Suppose Ave smoke 

 the interior of our 

 spectrophonic receiv- 

 er, and fill the cavity 

 with peroxide of ni- 

 trogen gas. We have 

 then a combination 

 that gives us good 

 sounds in all parts of 

 the spectrum (visible 

 and invisible), ex- 

 cept the ultra-violet. 

 Now, pass a rapidly- 

 interrupted beam of 

 lioht throuo'h some 

 substance whose ab- 

 sorption sjDectrum is 

 to be investigated, 

 and bands of sound 

 and silence are ob- 

 served upon exploring the spectrum, the silent positions correspond- 

 ing to the absorption bands. Of course, the ear can not for one mo- 

 ment compete with the eye in the examination of the visible part 

 of the spectrum ; but in the invisible part beyond the red, where 



"Proceedings of the Philosophical Society" of Washington, April 10, 1881. 



