362 Mr. J. P. Harrison on the Eelaiion of [Pcb. 14, 



Table VIII. 



Results of Actinometer-observations in May and July 1864. 



Month and 

 day. 



Mean solar 

 time. 



Mean results 

 in scale-di- 

 visions. 



Altitude of 

 sun. 



State of sky. 





li m 





o 





May 16. 



2 17 



28-3 



47 



Cloudless*. 



16. 



28 



21-4 



56 



Cloudless. 



16. 



14 



23-7 



57 



Cloudless. 



July 11. 

 5. 

 13. 



2 19 

 1 7 

 23 18 



46-7 

 36-6 

 39-3 



50 

 58 

 58 



Clear about sun. 



Clear. 



Cloudlesi. 



The mean tension of vapour in May was '30, in July '38. 



The last Table contains, in parts of scale, the results of groups of obser- 

 vations near midday and 2 p.m., on three days, in March, May, and July. 

 The maximum in each case occurs at the later hour. 



Table IX. 

 Actinometer-observations at 0'' and 2^. 



Month and 

 day. 



Mean solar 

 time. 



Mean result 

 in scale-di- 

 visions. 



Altitude of 

 sun. 



State of sky. 



March 24. 

 24. 



h m 



49 



1 32 



14-3 

 17-0 



o 



39 

 36 



Clear throughout. 

 Clear. 



May 16. 

 16. 



28 

 2 17 



21-4 

 28-3 



56 

 47 



Cloudless. 

 Cloudless. 



July 14. 

 14. 



23 37 

 2 13 



48-6 

 57-6 



59 

 50 



Cloudless. 

 Cloudless. 



The great accordance between the foregoing results renders it unnecessary 

 to adduce further evidence of the occurrence of maximum insolation some 

 considerable time after the summer solstice and after 5\ 



Increased solar radiation supposed to he due to the action of aqueous 

 vapour. — Herr von Schlagintweit, applying Professor Tyndall's discovery 

 of the absorptive properties of aqueous vapour to the phenomenon of inso- 

 lation, attributed the high readings of his solar thermometer, in certain 

 parts of India, to the fact that air, when highly charged with moisture, 

 impedes free radiation; that is to say, the air restores to the instrument 

 some portion of the heat which has been radiated off from it. 



A like cause has been recently assigned for the variations in temperature 

 which take place on clear nights in Madras under different tensions of va- 



* Compare ohservations on the same day at 0^ 28"" and 0^' 14™. 



