of Insolation to Atmospheric Humidity. 



393 



tions which were taken at or near the same elevation of the sun, in 

 the months of August and September in autumn, and in March and 

 April in spring, the value of the mean increase of the scale-readings 

 in the autumn proved to be about 100 per cent, greater than in the 

 spring*. 



The mean increase of the scale-readings in March and April was 19 '4. 



The mean increase of the scale-readings in Aug.and Sept. was 39*6. 



The difference is 202, at the same mean altitude of the sun. 



The means of the contemporaneous observations of the vacuum- 

 thermometer on the grass were as follows : — 



In March and April 70°«3 F. 



In August and September . . . 84°* 7 F. 



The difference is 14°*4. 



The mean tension of vapour in March and April was *23, and in 

 August and September *34. 



Mean Results of Actinometer-observations at Greenwich, March and 



April 1864. 



Month and 

 day. 



Mean solar 

 time. 



Mean results 

 in scale-di- 

 visions. 



Altitude of 

 sun. 



State of sky. 



March 23. 



15. 



18. 



18. 



24. 



15. 

 April 15. 



20. 

 March 24. 



h m 

 2 29 



22 23 

 2 9 



36 



1 32 



23 51 



2 26 

 2 28 

 49 



18-7 

 14-2 

 21-1 

 20-4 

 17-0 

 19-1 

 27-1 

 25-5 

 14-3 



o 



30 

 32 

 32 

 36 

 36 

 37 

 37 

 38 

 39 



Light cirri. 



Cloudless. 



Clear. 



Clear. 



Clear. 



Clear. Light cloud. 



Clear. 



Light cirri prevalent. 



Clear. 



Means. 





19-4 



35 



Clear. 



Mean Results of Actinometer-observations at Greenwich, August and 

 September 1864. 



Month and 

 day. 



Mean solar 

 time 



Mean results 

 in scale- di- 

 visions. 



Altitude of 

 sun. 



State of sky. 



August 30. 



September 14. 



14. 

 August 26. 



26. 



29. 

 5. 



h m 



3 26 



22 8 



22 12 



3 



2 55 



2 39 



3 3 



41-6 



43-3 

 34-7 

 38-3 

 32-4 



40-1 



41-7 



o 



30 | 



34 

 35 

 35 

 36 



36 \ 



39 



Cloudless (thunder 

 in evening). 



Sun free from cloud. 



Light cirri over sun. 



Sun free from cloud. 



Sun free from cloud. 



Clear (amount of 

 cloud in afternoon 9, 

 cirrocumuli, cirrus). 



Cloudless. 



Means 





39-6 



35 



Cloud generally pre- 

 sent. 



* See ' Greenwich Meteorological Eesults,' 1864, p. xxxviii. 



