286 PHYSICS. 



keep the arc steady aud poiuting in one direction. The two carbons are 

 X:)arallelbnt inverted, han ging with their points downward. -They have 

 no insulatiug material between them. Surrounding these, and in their 

 own phxne, is a flat coil of wire through which the main current circu- 

 lates. The trials with this lamp in Paris are said to have been success- 

 ful.— (iVY^fwre, xxii, 355, August, ISSO.) 



Eeynier has proposed an incandescent light in which the point of a 

 thin stick of carbon presses against a fixed carbon contact, while on it 

 laterally, a short distance above, a third piece of carbon makes contact. 

 The current enters by this lateral carbon and traverses the carbon pen- 

 cil to its pointed end, passing thence to the solid carbon support. The 

 pencil becomes thus incandescent, emitting most light at its point. Its 

 photometric value varies from five to twenty carcel burners, according 

 to the current. — {J. Fhys., viii, 400, December, 1879.) 



Siemens has presented to the Society of Telegrax)h Engineers a paper 

 on recent applications of the dynamo-current to metallurgy, horticulture, 

 and the transmission of i^ower. By means of an electric furnace made 

 of a black-lead crucible, the positive carbon entering through the bottom 

 and the negative through the cover, steel had readily been melted. 

 Using a moderate-sized dynamo-machine, consuming four horse-powers 

 and producing 36 webers of current — equal to a G,000 candle light — he 

 raises a crucible 20«="> deep to a white heat in less than half an hour, and 

 a kilogram of steel is fused in it in another half hour. This furnace 

 utilizes one-thirJ of the horse-power actually expended ; and as the effi- 

 ciency of the engine is one-fifth, that of the electric furnace is }^x}=^j. 

 As it takes theoretically 450 heat units to melt a pound of steel, the fur- 

 nace would require 450 x 15=0750 heat units to be expended, or about 

 the energy of a pound of coal. A ton of steel as ordinarily melted in an 

 air furnace requires 2i to 3 tons of coke ; in a regenerative furnace about 

 a ton. The electric furnace is economically su]>erior to the air furnace 

 and nearly equal to the regenerative furnace. When the paper was read, 

 a pound of broken files was melted in a cold crucible, by means of a cur- 

 rent of 72 webers, in fifteen minutes, and cast in a mould. With refer- 

 ence to the action of light on plants, the interesting experiments made 

 by him in this direction were detailed, and an account given of the ex- 

 periments now in progress to produce flowers and fruits without solar 

 aid. Under the third head of his paper, Siemens described his brother's 

 electric railway in Berlin, and its numerous applications. — {Xatiirc^ xxii, 

 135, June, 1S80.) 



Edison has finally determined upon the use of carbon filaments in his 

 incandescent lamps. These filaments are constructed by cutting with 

 a suitable punch, from a piece of Bristol board, a striii in the form of a 

 miniature horseshoe, about two inches in length and one-sixteenth of 

 an inch in width. These are laid in a wrought-iron mould, separated 

 from each other by tissue paper, and heated first by a gas flame and 

 then in a furnace to a white heat. After cooling, the charred fiber is 



