1883.] On the Dependence of Radiation on Temperature. 169 



the electro-dynamometer, is proportional to the resistance of the wire. 

 Hence the constant of the instrument and the resistance of the gal- 

 vanometer being known, the resistance of the platinum wire could be 

 calculated, as the current was varied by altering the number of cells 

 composing the battery. 



The measurements were made in all cases when equilibrium had 

 been established between the radiation and the energy of the current, 

 as evinced by the constancy of the readings of the electro-dynamo- 

 meter and galvanometer. 



Having made a rough preliminary series of experiments to test 

 the suitability of the method and apparatus, with satisfactory results, 

 on April 17th I made a second series, the results of which are 

 recorded in Table I. Column I gives the current in amperes passing 

 through the wire ; column II the difference of potential in volts 

 between the terminals as deduced from the readings of the galvano- 

 meter ; column III the rate at which the energy of the current was 

 converted into radiant energy, represented by the product of the 

 electromotive force and current, and therefore measured in volt- 

 amperes or watts ; column IV the resistance of the wire, being the 

 ratio of the electromotive force to the current ; column V the corre- 

 sponding temperature of the wire in degrees Centigrade. Finally, 

 column VI describes the condition of the wire as apparent to the eye. 



Table I. 



Length of wire 102 centims. Diameter 0*76 millim. 

 Temperature of room 65° F. 



I. 



II. 



III. 



IV. 



V. 



VI. 



Amperes. 



Volts. 



Watts. 



Ohms. 







2 91 



1-192 



3-468 



•4096 





Just warm to touch. 



3-999 



1-639 



6-555 



•4099 







5-738 



2-831 



16 -24 



•4933 



100° 





8-943 



5 -662 



50-64 



•6331 



282 





12 27 



9-536 



117*00 



•7772 



570 



Chars wood. 



16-66 



16-39 



273 -0 



•9838 



881 



Very dark red. 



13 19 



11-175 



147 -4 



•8472 



653 



Red heat. 



20 -90 



22 -052 



460-9 



1055 



1075 



Bright red. 



23-73 



26-82 



636-4 



1 -130 



1194 



Very bright. 



On April 18th, three further series of experiments were made, the 

 results of which are set forth in a similar manner in Tables II, III, 

 and IV. 



