292 



ELECTEICITY. 



means of a case, be protected from currents of 

 air. 



Electric Clocks. Van Bruyssel, of Berlin, has 

 recently made great improvements in the work- 

 ing of clocks by means of an electrical current, 

 so that from one regulating clock the time may 

 be indicated simultaneously upon clock-dials at 

 numerous and distant points in any town, dis- 

 trict, or country. Connected with the regulat- 

 ing clock, which beats seconds, is the shaft of a 

 commutator, which carries a pinion that gears 

 into a wheel in the arbor of the minute-wheel. 

 This gearing serves to rotate the shaft once in 

 two minutes. The commutator shaft carries 

 at its extremity an ivory cylinder, by which the 

 currents employed to actuate the clocks or 

 time-indicators will be constantly and alter- 

 nately changed from positive to negative, and 

 mce versa. The ivory cylinder is fitted with 

 two insulated metal disks, which are set con- 

 centric therewith, and dip respectively into 

 one of two mercury cups placed below them, 

 and brought into connection with the opposite 

 poles of a battery. Platinum wires from these 

 disks are led to one end of the cylinder and 

 laid parallel to its axis, and at opposite sides 

 of its periphery. Set around the cylinder, and 

 bearing upon its periphery at the part where 

 the wires are exposed, is a series of springs 

 made of rolled brass, which are affixed to the 

 back board of the commutator, and they num- 

 ber double the number of the groups or sections 

 of the clocks or time-indicators intended to be 

 worked. These springs are worked in pairs, 

 and each pair is connected by insulated wires 

 with their respective time-indicators. The 

 springs of each pair are so disposed that they 

 will both be in contact with the wires of the 

 ivory cylinder at the same time ; the one with 

 the wire of the near disk and the other with 

 that of the more distant. As, therefore, the 

 cylinder rotates, the circuit will be opened 

 through several pairs of springs with the sev- 

 eral indicators in regular succession, and the 

 required impulse will thereby be given through 

 electro-magnetic apparatus to the hands of the 

 indicators. Between the poles of the electro- 

 magnets is a permanent magnet, carried by 

 a vibrating forked arm, which embraces an 

 ordinary escape -wheel, and at each vibration 

 drives it forward the distance of one tooth. 

 This motion is by ordinary clock-gearing com- 

 municated to the hour and minute hands of the 

 indicator. But inasmuch as the platinum wires 

 transmit the one the positive and the other the 

 negative current, and, as their positions with 

 respect to the springs are alternately reversed, 

 a positive and a negative current will be alter- 

 nately transmitted to the distant time-indi- 

 cators. 



Cost of the Electric Light. Mr. Moses G. 

 Farmer has furnished to the Scientific Amer- 

 ican an estimate of the cost of the electric 

 light, produced by the electro-magnetic ma- 

 chine. He says that on a well-built machine, 

 which he examined in 1861, 1,100 foot-pounds 



per minute were required to keep it in motion, 

 when the circuit was open and the machine 

 doing no work; that when the machine was in 

 operation, then 3,200 foot-pounds per minute 

 were needed to maintain the same velocity of 

 rotation. Nearly all this excess of power (viz., 

 2,100 foot-pounds) was measured as electricity, 

 about two-thirds (say 1,300 foot-pounds) being 

 expended internally, beating the coils and mag- 

 nets, etc., and the balance, 800 foot-pounds, 

 measured as external useful effect. Had the 

 external resistance been greater, a greater pro- 

 portion of the expended power would have 

 appeared as useful. Suppose, however, that 

 only 800 foot-pounds per minute could be util- 

 ized by the machine and used for illuminating 

 purposes this would be the equivalent of 800 

 -i-15=53.33 candles, as the total power re- 

 quired (including friction, etc.) would be 3,200 

 -5-53.33=60, about 60 foot-pounds per minute 

 per candle. The author then proceeds to make 

 the following estimate, upon the supposition 

 that power is furnished, per horse-power, at 

 the rate of $180 per year of 313 days of 10 



hours each, or at the rate of J!J!*L 0.0575 



olo x 10 



(5f cents) per hour. 



" If only one-fourth of this power could be 

 utilized as light J^=550 candles would be 



the equivalent of one horse-power, and would 

 cost $0.0575-4-550 = $0.0001046, about one- 

 tenth of a mill per hour per candle, being about 

 one-tenth the cost of gas-light. 



" Let us for a moment take another view of 

 the matter. The average hourly consumption 

 of coal by a good steam-engine may be set down 

 at four pounds per hour per horse-power, = 

 (33,000 x 60)^-4=495,000 foot-pounds from one 

 pound of coal. Utilizing as electricity, and 

 thence light, one-fpurth part of this, we get 

 495,000-f-4= 123,750 foot-pounds, or as light, 



123 750 



lY^eo =13 ^ hour candle-lights from one pound 

 of coal, through the agency of steam-engine 

 and the magneto-electric machine. 



" With the thermo-electric battery I have been 

 able to develop 130,000 foot-pounds of electri- 

 city from one pound of coal=^^=144.4=to 



15x60 



about 144 candle-lights. 



" There is still another point of view worthy 

 our attention. Common gas-coal will yield 

 about ten thousand cubic feet of gas per ton. 

 This, at three hour candle-lights per cubic foot, 

 would give (3 xlO,000)-4-2,000=15 hour can- 

 dle-lights per pound of coal. About twenty- 

 five cubic feet of illuminating gas weigh one 

 pound. Hence one pound of gas, after it is 

 made from the coal, will yield a light equal to 

 that of a candle for seventy-five hours. One 

 pound of pure carbon, wholly burned to car- 

 bonic acid gas, yields 14,500 units of heat, 

 equal to 772 x 14,500=11,200,000 or Hi mil- 

 lions of foot-pounds of work : Hence, were the 

 total energy of one pound of pure carbon con- 

 verted into light, it would be equivalent to one 



