196 THE POPULAR SCIENCE MONTHLY. 



This result is confirmatory of the first. 



The audibility of the effect at a particular rate of interruption sug- 

 gests the explanation that the strip D had a normal rate of vibration 

 of its own. 



AVhen the frequency of the interruption of the light corresponded 

 to this, the strip was probably thrown into vibration after the manner 

 of a tuning-fork, in which case a to-and-fro vibration would be propa- 

 gated down its stem or central support to the strip (A). 



This indirectly proves the value of the experiment. 



The list of solid substances that have been submitted to experiment 

 in my laboratory is too long to be quoted here, and I shall merely say 

 that we have not yet found one solid body that has failed to become 

 sonorous under proper conditions of exj^eriment.* 



Experiments with Liquids. The sounds produced by liquids are 

 much more difiicult to observe than those produced by solids. The 

 high absorptive power possessed by most liquids would lead one to 

 expect intense vibrations from the action of intermittent light ; but 

 the number of sonorous liquids that have so far been found is ex- 

 tremely limited, and the sounds produced are so feeble as to be heard 

 only by the greatest attention and under the best circumstances of 

 experiment. In the experiments made in my laboratory, a very long 

 test-tube was filled wath the liquid under examination, and a flexible 

 rubber tube was slipped over the mouth far enough down to prevent the 

 possibility of any light reaching the vapor above the surface. Pre- 

 cautions were also taken to prevent reflection from the bottom of the 

 test-tube. An intermittent beam of sunlight was then focused upon 

 the liquid in the middle portion of the test-tube by means of a lens of 

 large diameter. 



EESULTS. 



Clear water No sound audible. 



Water discolored by ink Feeble sound. 



Mercury No sound heard. 



Sulphuric ether* Feeble but distinct sound. 



Ammonia '^ " " " 



Ammonio-sulphate of copper " " 



Writing-ink ' " 



Indigo in sulphuric acid " " 



CLloride of copper * " " 





The liquids distinguished by an asterisk gave the best sounds. 



Acoustic vibrations are always much enfeebled in passing from 

 liquids to gases, and it is probable that a form of experiment may be 

 devised which will yield better results by communicating the vibra- 

 tions of the liquid to the ear through the medium of a solid rod. 



* Carbon and thia microscope-glass are mentioned in ray Boston paper as non- 

 responsive, and powdered chlorate of potash in the communication to the French Acad- 

 emy (" Comptes Rendus," vol. cxl, p. 595). All these substances have since yielded 

 sounds under more careful conditions of experiment. 



