K. DOMESTIC AND HOUSEHOLD ECONOMY. 413 



and a half pounds, and it is constructed in sucli a manner that 

 it can be quickly put about the person, forming then a double 

 belt, attached in such a way that it can not possibly be dis- 

 placed. The whole process of rising from the mattress, attach- 

 ing it to the person, and entering the water was performed at 

 the Exhibition within three quarters of a minute. The limbs 

 are not confined, nor the motions of swimming interfered 

 with. It places within reach of every passenger an eflScient 

 and reliable life-preserver in any sudden emergency, and ap- 

 pears to be the most sensible and practical device of this kind 

 as yet invented. 



ELECTRICAL ILLUMINATION OF FACTORIES. 



In spite of the recent improvements in magneto-electric 

 machines, especially that of Gramme, electrical illumination 

 in factories has not displaced that by oil or gas to any ex- 

 tent. The Gramme machine has, however, been introduced, 

 with satisfactory results, into an establishment at Miilhausen. 

 The room illuminated is 196 feet by 98 feet. Four lamps, 

 on Serrin's plan, properly distributed, are employed, each run 

 by a separate magneto-electric machine requiring about two- 

 thirds horse-power to work it. The carbon points need 

 changing every three hours. The cost for the four lamps 

 per hour is about twenty cents. During two months of use 

 no diminution of intensity has been noticed, and the illumi- 

 nation afforded has been steady and superior in brilliancy to 

 that from any other source. The magneto-electric machines 

 cost about $300 apiece, or the four arranged, complete, about 

 11600. Laboulaj^e gives the following table of the compar- 

 ative cost of this and other methods of illumination : 



Consumption per Cost per hour 

 Source of light. hour for 1-steariu for a 700-steariu 



candle-light. caudle-light. 



Electricity, by magneto-electric machine. 0.10 to 0.20 francs 



Electricity, by galvanic battery 3.00 to 5.00 



Coal-gas." 15 litres 3.20 



Light petroleum 4.52 grammes 3. 8 



Rape-seed oil 5.18 " G.IO " 



Tallow candles 10.55 " 12.60 " 



Stearin candles 10.40 " 2G.20 " 



Wax candles 8.2G " 32.40 " 



Efforts to distribute the current from a sinojle machine to 

 several lamps have not proved practically successful, by rea- 





5 " 



