PHYSICS. 



By GEORGE F. BARKER, 



Peofessor. of Piiysics in the Univeksity of Pennsylvania, PuiEADELraiA. 



GENERAL. 

 The year 1878 has witnessed a considerable progress in the 

 science of Physics. A noteworthy occurrence is the address 

 delivered at Glasgow, by Dr. C. W. Siemens, " On the Utili- 

 zation of Heat and other Natural Forces," because he discuss- 

 es in it the available sources of power when the supply of 

 coal shall fail. Using at some central station water- or wind- 

 power to drive dynamo-electric machines, the current gener- 

 ated could easily be reconverted into power where it is want- 

 ed, either for mechanical or other purposes. For light, for 

 example, from 100 horse-power 125,000 candle-lights would 

 be obtained, equivalent to 6250 Argand burners of 20 can- 

 dles each, consuming six feet per hour, or 37,500 cubic feet 

 for all. To produce this amount of gas, 3f tons of coal are 

 required, while to produce the 100 horse-power only as many 

 hundred-weights are necessary. In the case of Niagara, he 

 computes that 100,000,000 tons of water fall every hour 

 through a vertical height of 150 feet, giving 10,800,000 

 horse-powers, the only result being an elevation of the tem- 

 perature of the water by one fifth of a degree Centigrade. 

 To pump back the water would require an annual expendi- 

 ture of 266,000,000 tons of coal (at four pounds coal per 

 horse-power per hour) an amount equal to the total coal 

 consumption of the world. Since by electric means one 

 half the energy supplied at the central station may be re- 

 covered at the distant one, the economy is greater than in 

 the steam-eno-ine. Greater care in the use of w r ater- and 

 wind-power is now possible, and the intermittent character 

 of wind-power may be made permanent by using it to raise 

 water into a reservoir. Moreover, the force of falling water 

 in its descent from reservoirs and lakes, to supply our large 

 cities, miejht be utilized on the way bv driving turbines, 



