JosepJi Baxcndell, F.R.S. 45 



radiation on cloudless days, has its time of maxima and 

 minima corresponding with those of the curve representing 

 the mean monthly diurnal ranges of the magnetometer. 

 4th — It seems probable that the heating rays of the sun 

 consist of two kinds differing considerably in intensity, and 

 being subject to periodical changes, the times of maximum 

 of one kind and those of minimum of the other, corresponding 

 respectively to the time of maximum frequency of solar 

 spots. 5th — That the oscillations of mean daily tempera- 

 ture are intimately connected w^ith the changes which take 

 place in the earth's horizontal magnetic intensity. The 

 results derived from the Greenwich observations he states 

 to have been anomalous and unsatisfactory. — " On Solar 

 Radiation, Part II." He applies to his first paper a 

 correction for the difference of meridian altitude of the sun 

 in the different months of the year. He also discusses some 

 of Mr. Mackereth's observations at Eccles in connection 

 with the subject. From his results he derives the following 

 conclusions : ist — The power of the atmosphere to absorb 

 the heating rays of the sun is much greater in the summer 

 than in the winter months, and depends apparently upon the 

 amount of aqueous vapour which it contains. 2nd — Clouds 

 and haze are less prevalent during the day, or their power 

 to intercept the heating rays of the sun is less active in the 

 spring and autumn than in the winter and summer months. 

 3rd — Observations of solar radiation made with a black 

 bulb thermometer to be of value ought to be taken with the 

 radiation thermometer placed at the same height above the 

 ground as the shaded maximum thermometer with which it 

 is compared ; but while freely exposed at all times to direct 

 sunlight, it ought to be protected as much as possible from 

 disturbing influences. 4th — Solar radiation observations 

 made on a plan similar to that adopted at Oxford, show that 

 the calorific intensity of the sun's light continued to diminish 

 during the years 1865-66, when the frequency of solar spots 



