MEMOIR I.] THE RADIATIONS OF IGNITED BODIES. 



43 



multaneously noted, 

 and then the voltaic 

 current was stopped. 



Sufficient time was 



f ,, 

 now given for the 



needles of the multiplier to come back to zero. This 

 time varied in the different cases, according to the in- 

 tensity of the heat to which the pile had been exposed ; 

 in no instance, however, did it exceed six minutes, and 

 in most cases was much less. A little consideration will 

 show that the usual artifice employed to drive the needles 

 back to zero by warming the opposite face of the pile was 

 not admissible in these experiments. 



The needles having regained their zero, the platinum 

 was brought again to a given temperature, and the ex- 

 periment conducted as before. The following table ex- 

 hibits a series of these results. 



In this table the first column gives the temperatures 

 of the platinum in Fahrenheit degrees ; the second and 

 third, two series of experiments expressing the arc passed 

 over by the needle at the close of a radiation lasting one 

 minute, each number being the mean of several suc- 

 cessive trials, and the fourth the mean of the two. It 

 therefore gives the radiant effect of the incandescent 

 platinum on the thermo-multiplier for the different tem- 

 peratures. 



Of course it is understood that I here take the angu- 



