148 



MR. JOSEPH BAXENDELL 



which might be necessary in a more exact inquiry in con- 

 sequence of equal increments in the difference between 

 sun and shade temperatures not corresponding exactly to 

 equal increments of calorific intensity of the sun^s rays. 

 This Table gives for every fifth degree of altitude the calo- 

 rific intensity of sunlight, the intensity of the light on 

 entering the earth^s atmosphere being taken = i . If the 

 rate of emission of heat from the sun were constant, and 

 change of season exercised no influence on the absorptive 

 power of the atmosphere, the quotient obtained by dividing 

 the mean value of solar radiation on clear days in any 

 month, by the number in this Table corresponding to the 

 sun's meridian altitude in the middle of the month, would 

 be a constant quantity. The results given in the following 

 Table will, however, show that, according to the Oxford 

 observations, this is by no means the case : — 





Mean amount of 

 solar radiation 

 on clear days. 



Meridian 



altitude of the 



sun on the 15th 



of the month. 



Proportion 



of light 

 transmitted. 



Number in 



first column 



divided by 



number in 



third column. 



January 



February . . . 

 March 







135 



17-6 

 17-8 



20*3 

 19'2 



i8-i 

 19-2 

 19*6 



20*0 

 181 



15-6 

 130 



t 

 17 6 

 25 32 

 36 3 

 47 57 

 57 4 

 61 34 



59 50 

 52 23 

 41 22 

 29 48 

 19 48 

 14 59 



•37 



•51 

 •61 



•68 

 '71 

 •72 

 •72 

 •69 



•65 

 •56 

 •43 

 •33 



36-5 

 34-5 

 292 

 298 

 27*0 

 25-1 

 26*7 

 28-4 

 30-8 

 32-3 

 36-3 

 39*4 



April 



Mav 



June 



July 



August 



September ... 



October 



November ... 

 December ... 



The numbers in the last column show that the power of 

 the atmosphere to absorb the heating rays of the sun is 

 much greater in the summer than in the winter months, 

 the maximum effect taking place in the month of June, 

 when the sun attains his greatest meridian altitude, and 

 the minimum in December, when his meridian altitude is 



