438 Sir James Dewar [Jan. 28, 



From (2) it follows that at about 11.30 p.m. the additional radiation 



due to the full moon was — - of the value for the sky zone alone, 

 2-50 J 



0^45 x 2-50 = f h bkck bod c 



2*50 2*40 J 



From (3) it follows that at 1 a.m. the additional radiation due to the 



full moon was — — - of the sky zone alone ; but as the skv was then 

 2*2o 



2*25 



oTqa °^ ^lack a ^ ^° ^* (equivalent to a black body temperature of 



- 17° C, see curve of Fig. 5), the moon radiation was X ° = 



& J 2-25 2-90 



0-241 of the black at 0° C. 



Now it has been shown (p. 420) that the radiation available to 

 the thermoscope of 4" 9 sq. cm. area per half minute from black at 

 15° C. is of the order of 0*0071 calorie. This would be 0*0064 

 calorie from black at 8° C. ; 0*0059 calorie from black at 2 C C. : and 

 * 0057 calorie from black at 0° C. The moon's emission per minute 

 into an area of 4*9 sq. cm. would thus appear to be 



from (1) 2 x 0*116 x 0*0064 = 0*00148 calorie 



from (2) (11.30 p.m) 2 x 0*1875 x 0*0059 = 0*00221 calorie 



from (3) (1 a.m.) 2 x 0*241 x 0*0057 - 0*00275 calorie. 



In terms of calories per minute per sq. cm. of absorbing surface 

 the moon's emission is thus 0*0003 from (1), 0*00045 from (2) 

 and 0*00056 from (3). The value deduced from (1) is of less 

 significance than those obtained from (2) and (3) owing to the three 

 hours' interval between the sky and moon observations. 



Since the luminous emission per unit area from the moon is only 

 1/400,000 of that of the sun, it must be admitted that these values 

 appear to be very high. As already stated, the construction of the 

 instrument at the time was very imperfectly developed, and the 

 results are probably therefore only directional. 



Pressure Increase by Radiation into Charcoal 

 at Low Gas Pressures. 



The response due to radiation into gas-charged charcoal can be 

 measured not only at atmospheric pressure as already described, but 

 down to pressures of less than one-millionth of an atmosphere. 



These small gas pressures were measured on a Macleod gauge to 

 which was sealed a bulb containing 1 gramme of charcoal. After 

 initial evacuation to below 0*0001 mm. with the charcoal at 300° C, 

 the bulb was cooled in liquid air. Small measured volumes of pure 

 air, nitrogen and hydrogen respectively were then admitted. The 



