44S 



RECENT PROGRESS IN PHYSICS. 



Micss found by his formula 0.1133 instead of 0.1106 — a difference 

 so small as not to require further examination. 



In a similar manner he determined the heating capacity of other 

 metals, and found as follows : 



The first of these columns of numbers gives the capacity of metals 

 for the development of heat — that is, the relative height of tem- 

 perature different kinds of wire of the same thickness would reach, if 

 they were fastened together end to end, and an electric battery dis- 

 charged through them. 



Multiplying the heating capacities of metals by their specific weights 

 and specific heats, the numbers are obtained, which show the quan- 

 tities of heat set free by the same discharge in equally thick wires. 



Again, taking platinum for unity, we must divide all the products 

 found by the specific weight and specific heat of platinum. In 

 this manner the numbers of the second column were obtained. 



This series of numbers shows the ratio of the quantities of heat set 

 free in different kinds of wires of equal diameters when, being 

 fastened end to end, they discharge an electrical battery. 



Comparing these numbers with the retarding forces given on page 

 446 we see that they are almost precisely equal, the difference being 

 so small as to be explained by the fluctuating values of capacity for 

 heat and specific weights in connexion with errors of observation ; 

 hence, the retarding force of different metals is (cmteris pat'ibus) in the 

 same proiwrtion as the quantity of heat set free in the ivires hy the 

 electrical discharge. 



Hence it follows further, that the relative electrical heating capacity 

 of a metal may be found by dividing its electrical retarding force by 

 its specific weight and capacity for heat ; multiplying by the 

 specific weight and capacity for heat of platinum, when the heating 

 capacity of platinum is = 1. 



§ 50. Entire QUANTITY op heat produced by tub discharge. — Vms- 

 selman de Heer made use of the experiments given above for deter- 

 mining the entire quantity of heat vv^hich an electrical dischager 

 generates (Pog. Ann. XLVIII, 292), by making in Riess formula a 

 transformation which is in perfect harmony with the modification 

 given in page 439. 



He showed in this way what should be the length L of a platinum 

 wire of given thickness which should offer to the discharge the same 



