jf_ /,;,.,.,/_ Weber's Law qf Thermal Radiation. 14 1 



the accompanying table of results, in which the Becond colnmn 

 oontaina the differences of the rates of cooling of the two 

 thermometers, and in which T l *=287 , 'i 



In this case, also, the value of a=*0043 is very much too 

 Mnall and the value o{ 007 is required to Batifify the condition 

 of (4), which requires the last member to be a constant. 



B. From what precedes it is seen that the value of a in 

 Weber's formula which satisfies (4) with Schleiermacher's 

 experimental results, in which the rate of loaing heat in the 

 heated body is determined by the electric method, does not 

 satisfy it where the rate of the loss of heat is ascertained from 

 the observed rate of cooling of a body of known heat capacity, 

 or by the deviations of khe galvanometer needle of the thermo- 

 pile'; and that the value of a required in the last two cases is 

 much greater than in the former. It also appears that the 

 value of a required in the last two cases increases with decrease 

 of temperature. For in the case of the table of § 6, in which 

 the range of temperature, neglecting the first two places, is 

 from 3S9'6° to 569-0°, the mean being 479 6°, and through 

 which the values of the last column of the table are approxi- 

 mate! v equal, the value of 0=-OO59 is required, while in the 

 case of the table of § 5, in which the range of temperature is 

 from 353° to 513°, the mean being 433°, the value of a required 

 is -0064. Again, in >< 7 where the average temperature is only 

 337-7, the still greater value of ^ = '007 is required to make the 

 numbers of the last column approximately equal. 



That the value of a in Weber's formula must increase with 

 decrease of the temperature in Kosetti's experiments is seen 

 from the values in the last column of the table of § 6, in which 

 the numbers increase for the lower and decrease for the higher 

 temperatures, which indicates that the value of a in the for- 

 mula must be greater for the lower than for the higher temper- 



atures 



9. It has been shown in J< 7, paper A, that if we multiply the 

 rates of cooling in the experiments of Dulong and Petit by 

 04516, we get the rate of losing heat by radiation from each 

 unit of surface. Hence, multiplying the mean value of 

 CFT^T, in the last column of the table of § 5, which is 

 1-001, into 04516, we get 



273 Ce 273a =0'452 



the value of F being unity in this case, and the first member 

 of this equation is the expression of the rate of radiating heat 

 from each unit of surface at the temperature of T 1 = 273° 

 which in ^7, paper A. was denoted by m and found to be 

 0-718S from Dulong and Petit's formula with a= 1*0082, and 

 0-3296 from Stefan's law with e=±'2. 



