Oct. 24. 1878] 



NATURE 



67: 



Electricity as a motive power, until now, has been a 

 comparative failure, as 90 per cent, of the battery has 

 been wasted. Mr. Edison has devised a novel elec- 

 trical machine which he calls the harmonic engine, in 

 which 90 per cent, of the power is realised. With two 

 small electro-magnets and three or four small battery 

 cells, sufficient power is generated to drive a sewing 

 machine or pump water for household purposes. This 

 engine, which is represented in Fig. i, consists of a 

 fork ■2\ feet long, made of 2-inch square steel. The 

 curved part of the fork is firmly keyed in a solid casting 

 which is bolted to a suitable foundation, and to each arm 

 of the fork is secured a 35 lb. weight. Outside of and 

 near the end of each arm is placed a very small electro- 

 magnet. These magnets are connected with each other, 

 and with a commutator that is operated by one of the arms. 

 The arms make thirty-five vibrations per second, the 

 amplitude of which is \ inch. Small arms extend from 



the fork arms into a box containing a miniature pump 

 having two pistons, one piston being attached to each 

 arm. Each stroke of the pump raises a very small quan- 

 tity of water, but this is compensated for by the rapidity 

 of the strokes. Mr. Edison proposes to compress air 

 with the harmonic engine, and use it as a motive agent 

 for propelling sewing machines and other light machinery. 

 The power must be taken from the fork arms so as not 

 to affect the synchronism of their vibrations, otherwise 

 the engine will not operate. 



In quadruplex telegraphy it is vital to the working of 

 the system to perfectly balance the electrical current. 

 The common method of doing this is to employ a rheostat 

 containing a great length of resistance wire, more or less 

 of which may be thrown into or cut out of the electrical 

 circuit by inserting or withdrawing plugs or keys. This 

 operation often requires thirty minutes or more of time 

 that is or might be very valuable. To remedy this difficulty 



Fig. 3. — Edison's Phonomoter. 



Mr. Edison has devised the instrument represented in 

 Fig. 2, I being a perspective view and 2 a vertical sec- 

 tion. A hollow vulcanite cylinder A is screwed on a boss 

 on the brass plate B. Fifty disks— cut from a piece of 

 silk that has been saturated with sizing and well filled 

 with fine plumbago and dried — are placed upon the boss 

 of the plate B, and are surmounted by a plate C, having a 

 central conical cavity in its upper surface. A pointed 

 screw D passes through the cap E at the top of the 

 cylinder A, and projects into the conical cavity in the 

 plate C. The screw is provided with a disk F, having a 

 knife edge periphery which extends to the scale G, and 

 serves as an index to show the degree of compression to 

 which the silk disks 'are subjected. The instrument is 

 placed in the circuit by connecting the cap E with one end 

 of the battery wire and the plate B with the other end. 



The principle of the instrument is identical with that 

 of Mr. Edison's carbon telephone. The compression of 

 the series of disks increases conductivity ; a diminutioi 



of pressure increases the resistance. Any degree of 

 resistance within the scope of the instrument may be had 

 by turning the screw one way or the other. In this in- 

 strument the resistance may be varied from 400 to 6,000 

 ohms, and any amount of resistance may be had by 

 increasing the number of silk disks. 



The thermo- telephone, although at present without 

 special practical value, is certainly a novelty. It consists 

 of a thermopile having placed in its collecting funnel a 

 hard rubber disc. A sound made in front of this disc 

 is heard in a receiving telephone connected with the 

 thermopile. 



The rationale of this is at once apparent when a strip 

 of hard rubber is placed against the lips and bent, so 

 that the strip will be alternately concave and convex. 

 The difference in temperature is very perceptible, the 

 convex surface being cold and the concave surface warm, 

 and, however rapid the vibrations which render the sur- 

 faces alternately convex and concave, the result is the same. 



