ON SOLAR RADIATION. 145 



had made at Eccles with an ordinary black-bulb thermo- 

 meter placed on the south side of the shade-stand, four 

 feet above the ground. The thermometer had been duly 

 compared at the Kew Observatory. I was chiefly induced 

 to make these reductions because the discussions of Mr. 

 Baxendell on the subject were from observations made at 

 Oxford by means of a thermometer placed somewhat simi- 

 larly to mine, at least as mine was placed during the five 

 years I have reduced. 



Taking the differences between the mean maximum 

 black-bulb reading in the sun, and the mean maximum 

 reading in the shade, for each month, we find two maxima 

 (one in May, and another in August) and two minima 

 (one in June, and another in December). 



In order to project the gradual rise and fall of solar radi- 

 ation for each month, I have adopted the form of table 

 presented by Mr. Vernon in his reductions of similar obser- 

 vations. Thus, if we take the difierences between one month 

 and the succeeding one, we find the following values : — 



o 



January to February -f"2^'^° 



February to March 4-2*98 



March to April +3'i6 



April to May -f-i'i4 



May to June — o'8o 



JunetoJuly +0*38 



July to August +0*56 



August to September — 1*48 



September to October —528 



October to November — 2*26 



November to December — 3'o6 



December to January +186 



The foregoing Table shows a very regular though rapid 

 increase of the amount of solar radiation from January 

 till April, which is only slightly exceeded in May. We have 

 then a slight decrease, and afterwards another maximum 

 in August. Then follows a very rapid decrease to October, 

 which continues, though not so rapidly, to the end of the 

 year. This Table shows that the observations at Eccles 



SER. III. VOL. IV. L 



