PHYSICS. 285 



have the same intensity in each. The action of the metal is then indi- 

 cated on the graduation of the sonometer. — {Phil. Mag., V, viii, 50, 551, 

 554, 1879 ; ix, 123, 1880; J. Phys., viii, 353, 1879; ix, 370, 389, 393, 1880; 

 Ann. Chim. Phys., V, xix, 5C1, April, 1880.) 



4. Electric sparlc and light. 



Spottiswoode has experimented on the use of the alternating current 

 of a De Meritens magneto-electric machine for exciting the induction 

 coil. He used a coil giving a 50*=" spark, the reversals being 1,300 per 

 minute; no interrupter was therefore needed. Under these conditions 

 sparks were obtained only 18°"" long, but they were as thick as an or- 

 dinary- i^encil. They showed a brilliant point at each extremity of a 

 tongue of yellow flame. When the current passed freely no spark 

 proper appeared ; but by blowing on one side, brilliant si)arks may bo 

 made to pass. — {Phil. Mag., V, viii, 390 ; J. Phys., ix, 37, 1880 ; Nature, 

 xxi, 433, March, 1880.) 



Farmer has called attention to the fact, as a contribution to the his- 

 tory of electric lighting by incandescence, that in Jul}-, 1859, his house 

 in Salem was lighted every evening by a subdivided electric light. A 

 galvanic battery of three dozen six-gallon jars in the cellar furnished 

 the electric current. On the mantel in the parlor were two electric 

 lamps, either of which could be lighted at pleasure or both at once by 

 simjily turning a little button. The light was soft, mild, agreeable to 

 the eye, and more delightful to read or sew by than any light ever seen 

 before. It was discoiitinued on account of theexi^euse. On the cost of 

 electric light as compared with gas Farmer says : " On the average one 

 pound of illuminating gas will, if burned in an hour in five different 

 burners, give fifteen candle lights to each burner, or seventh-five can- 

 dle lights in all. One jiound of illuminating gas possesses a sufficient 

 store of energy to enable it to give out by combustion from 18,000 to 

 21,000 units of heat, or the equivalent of from 13,000,000 to 10,000,000 

 foot-pounds of work. This, if burned in an hour, would average from 

 200,000 to 260,000 units of w^ork per minute, or say from 3,000 to 3,500 

 foot-pounds per minute per candle light. Now a very large electric 

 light, say ten thousand candles, does not consume more than 15 or 

 20 foot-pounds of energy jier minute per candle light. So it might not 

 seem very extravagant to expect that one i)ound of gas per hour could 

 be burned in a suitable furnace under a proper boiler, and steam be taken 

 from this boiler to a steam-engine, and this engine drive a magneto- 

 electric machine which should suj^ply electricity to five electric lamps 

 that would shed forth more light than could be given by five of the best 

 gas lamps known, each lamp consuming at the rate of one-fifth of a 

 pound of the best illuminating gas per hour." — {Am. J. Sci., Ill, xvii, 

 65, January, 1879.) 



Jamin has constructed a modification of the Jablochkoft" candle, in 

 which he has made use of the electrodyuamic action of a coil of wire to 



