52 Emission and Transmission of Heal 



vessel G G contains a horizontal 

 wheel R R having spokes formed of 

 cords which rub as the wheel re- 

 volves against the lower surface of 

 the disc E. This wheel is driven by 

 Fig. xey the pinion P, the gear U and the 



crank M of which the shaft passes 

 through the stuffing box H. 



By means of this apparatus I was able to renew 1600 times 

 per minute the water in contact with the surfaces of the metallic 

 disc. 



With water at very nearly 24 Cin the open vessel, and at 

 the atmospheric temperature in the inner vessel, and employing 

 discs of lead of twenty and fifteen millimeters in thickness, the 

 duration of equal amounts of heating of the water in the interior 

 vase was 500 seconds for the first disc and 380 for the second, 

 this last figure only differs by five seconds from three-quarters of 

 the first. 



We may therefore consider the law of thicknesses as having 

 been proven by direct experiment. 



In these experiments the mean temperature of the outer bath 

 was 24.04 Cand only differed from the extreme temperatures 

 by a small fraction of a degree. The excesses of temperature at 

 the beginning and the end of the experiment were 8.91 Cand 



9-55 C. 



Then the quantity of heat transmitted through the 20 mm. 

 disc was .000294 per minute; the weight of water enclosed in the 

 vessel increased by the weight of the vessel multiplied by its spe- 

 cific heat being 3.287 kilograms, the quantity of heat which 

 would be transmitted through the disc for a difference of i C 

 would equal, .000294X3. 287=. 000966 and as the surface of the 

 disc was .005026 square meters the quantity which tinder the 

 same circumstances would be transmitted per square meter would 

 equal, .OOO966X .mr^rsr =0.192 and for a disc one meter thick, 

 and during one hour would equal .192 X .02 X 3600=13.83* and 

 this figure is the conductivity of the metal. 



833. Then if we admit the correctness of the relative con - 



*H3 B. T. U. per hour per square foot per i F. per I inch thickness. 



