Hutchins and Pearson — Air Radiation. 285 



3to 



Calling D the deflection and t the temperature, the equation 

 of this curve may be written, 



From which, using three observations, we obtain, 



D = -7185 t + '486 f (10- 2 ) + -96 f (10~ 5 ) 

 the logarithmic coefficients being 



log A = 9-856448 -10 

 log B = 7-687127 — 10 

 log C = 4-984735 — 10 



From the above the relative ratio of air radiation per degree 

 at different temperatures may be found. 



For t = 1°, we have dB/dt = 0*728 

 For t = 100°, dD/dt = 1*98 



Hence the radiation per degree at 100° is 1-98/0-728 = 2*72 

 times greater than at 1°. 



There remains before computing the value of the radiation 

 constant to find the temperature gradient of the hot air column 

 in the line of sight ; laterally, the central portion of the air 

 column only was used and no correction in that direction is 

 required. A thermal junction of thin copper and iron wires 

 was moved by steps through the heated air column, and the 

 readings of a galvanometer, through which the junction was 

 connected, noted. The edge of the opening in the air chimney 

 being called 0, its center would be at 5. The following read- 

 ings were obtained : 



