152 MR. JOSEPH BAXENDELL 



purpose the table in the article on climate in the ' Encyclo- 

 paedia Britannica ^ already referred to, we obtain the fol- 

 lowing corrected numbers : — 



January 159 



February 2*66 



March 2"6o 



April 3 00 



May 2*42 



June 2'70 



July 2-39 



August 2*59 



September yiy 



October 2'63 



November 2*44 



December i'29 



The highest values occur in April and September, the 

 months in which the diurnal oscillations of the declination 

 magnetometer are greatest, and the general course of the 

 numbers indicates that clouds and haze are less prevalent, 

 or less dense, or their power of absorbing the heating rays 

 of the sun less active in the spring and autumn than in 

 the winter and summer months ; and in connexion with 

 this it may be remarked that the rate of change in the 

 difference between the temperature of the air and the tem- 

 perature of evaporation is greatest in the months of April 

 and September. 



Since the first part of this paper was printed in the So- 

 ciety's ^Proceedings,' Mr. Mackereth, F.R.A.S., has com- 

 municated to the Physical and Mathematical Section the 

 monthly results of his Solar-radiation Observations made 

 at Eccles during the five years 1862-66. As these obser- 

 vations were made with a black-bulb thermometer placed 

 somewhat similarly to that used at Oxford, and as the 

 series extends two years beyond the Oxford series, it was 

 evidently very desirable to examine how far they confirmed 

 the conclusions derived from the Oxford observations. 

 The mean annual values of solar radiation having been 

 deduced from the monthly means, and Mr. Mackereth 

 having kindly supplied me with the annual mean tempe- 

 ratures of the air and of the dew-point, they were treated 

 on the plan employed in discussing the Oxford observations. 



