84 ATOMS, MOLECULES, 



weak waves can produce effects which strong waves are 

 incompetent to produce ? This is a feature character- 

 istic of periodic motion. In the experiment of singing 

 into an open piano already referred to, it is the accord 

 subsisting between the vibrations of the voice and those of 

 the string that causes the latter to sound. Were this 

 accord absent, the intensity of the voice might be quin- 

 tupled, without producing any response. But when 

 voice and string are identical in pitch, the successive 

 impulses add themselves together, and this addition 

 renders them in the aggregate powerful, though in- 

 dividually they may be weak. In some such fashion 

 the periodic strokes of the smaller ether waves accumu- 

 late, till the atoms on which their timed impulses im- 

 pinge are jerked asunder, and what we call chemical 

 decomposition ensues. 



Savart was the first to show the influence of musical 

 sounds upon liquid jets, and I have now to describe an 

 experiment belonging to this class, which bears upon 

 the present question. From a screw-tap in my little 

 Alpine kitchen I permitted, an hour ago, a vein of water 

 to descend into a trough, so arranging the flow that the 

 jet was steady and continuous from top to bottom. A 

 slight diminution of the orifice caused the continuous 

 portion of the vein to shorten, the part further down 

 resolving itself into drops. In my experiment how- 

 ever the vein, before it broke, was intersected by the 

 bottom of the trough. Shouting near the descending 

 jet produced no sensible effect upon it. The higher 

 notes of the voice, however powerful, were also ineffec- 

 tual. But when the voice was lowered to about 130 

 vibrations a second, the feeblest utterance of this note 

 sufficed to shorten, by one-half, the continuous portion 

 of the jet. The responsive drops ran along the vein 

 pattered against the trough, and scattered a copious 



