,42 THE POPULAR SCIENCE MONTHLY. 



The loudness of the sound emitted through the directing tube, F, is 

 dependent on the size of the diaphragm and the power which moves it. 

 The former of them is made very large, and the latter can be mcreased 

 to many hundred pounds' pressure. 



The Harmonic Engine.— This instrument is shown in Fig. 36. Mr. 

 Edison claims that ninety per cent, of the power derived from the bat- 



FiG. 36. 



tery is utilized through its agency. The parts of the machine are : a 

 tuning-fork of large dimensions, vibrating about thirty-five times a 

 second, and carrying on each arm a weight of thirty-five pounds. The 

 amplitude of the vibration is about one-eighth of an inch, and he vibra- 

 tions are sustained by means of two very small electro-magnets, placed 

 near the end of each arm. These magnets are connected in circuit with 

 each other, and with a commutator worked by one of the arms 



Small branches extend from the fork-arms into a box contaming a 

 miniature pump having two pistons, one attached to each arm Each 

 stroke of the pump raises a very small quantity of water, but this is 

 compensated f o'r by'the rapidity of the strokes Mr. Edison proposes 

 to compress air with the harmonic engine, and use it as a motor foi 

 propelhng sewing-machines and other light machinery. It appears to 

 be considerably m advance of other electric cngmes, and through its 

 agency electricity may yet become a valuable motive-power. 



