Aqueous Vapour on Terrestrial Radiation. 



65 



the air. It then occurred to me to ascertain whether the quantity 

 of vapour appeared to influence the variation of diurnal tempera- 

 ture, irrespective of the action of clouds. For this purpose I se- 

 lected from the observations those days on which the sky was 

 almost free from clouds, and noted the march of the thermometer. 

 The varying power of the sun in its annual course from north 

 to south prevents any immediate comparison of the gain of heat 

 during the day being available to test the influence of the watery 

 vapour in absorbing the sun's heat. But the loss of heat at 

 night being essentially dependent on the radiation from the earth 

 into space through the air, a reliable standard was here to be got. 

 I accordingly calculated the fall of temperature from 6 h 40 m p.m., 

 Madras time, to 5 h 40 m a.m. next morning for the days selected 

 as sufficiently celar; at the same time the mean tension of va- 

 pour during the night was also calculated, and the temperature 

 at 6 h 40 m p.m. noted. The results, arranged according to the 

 quantity of vapour, for the years 1841, 1842, 1843, and 1844 are 

 given in the annexed Table : — 



1844. 



1844 (continued). 





Fall of 



Thermo- 



Percentage 



! 



Fall of 



Thermo- 



Percentage 



Tension of 



thermome- 



meter at 



of clear 



Tension of 



thermome- 



meter at 



of clear 



vapour. 



ter, 6h 40m 

 to 17h40m. 



6h 40m. 



sky. 



vapour. 



ter, 6h 40m 

 to!7h 40m. 



6h 40m. 



sky. 



inch. 









inch. 









100 



2-7 



87-2 



•98 



•71 



7°2 



81-2 



•92 



'97 



3-6 



87-4 



•92 



•71 



8-5 



82-0 



1-00 



•95 



4-6 



86-4 



•91 



•71 



76 



81-3 



•92 



•94 



4-8 



86-4 



•98 



•71 



5-4 



79-0 



•99 



•94 



4-5 



86-1 



•96 



•69 



5-5 



77-8 



•96 



•94 



4-8 



85*8 



•90 



•69 



7-7 



81-2 



1-00 



•93 



4-5 



86-5 



1-00 



•68 



6-3 



77-7 



•97 



•92 



5-0 



86-3 



•99 



•67 



7-6 



77-7 



* 100 



•92 



6 1 



870 



•96 



'67 



7'5 



77-7 



•91 



•92 



4-2 



86-3 



•96 



'67 



11-2 



81-8 



1-00 



•91 



50 



85-5 



•95 



'67 



76 



790 



•91 



•91 



4-7 



86-5 



'97 



'67 



73 



79-4 



•98 



•91 



52 



857 



•94 



•65 



9-5 



78-0 



1-00 



•90 



52 



86-7 



•95 



•65 



8-6 



' 78-4 



•94 



•90 



3-4 



86-1 



•97 



•64 



8-6 



77-0 



•96 



•89 



5-3 



86-3 



•98 



•64 



7-5 



77-2 



•96 



•86 



6-2 



84-6 



•90 



•63 



9-5 



80-5 



1-00 



•81 



5-7 



83-5 



•93 



1 -63 



7-6 



773 



•95 



•81 



6-8 



84-0 



•94 



j -62 



91 



772 



100 



•80 



50 



83-3 



•91 



•62 



6-9 



77-8 



1-00 



•77 



M 



83-2 



100 



•61 



9-6 



77-6 



1-00 



'76 



66 



82-1 



•97 



•60 



9-6 



78-0 



1-00 



75 



5-8 



80-2 



•99 



•59 



12-2 



79-9 



100 



•74 



75 



81-8 



•94 



•59 



8-1 



751 



1-00 



•74 



6-7 



81-8 



•98 



•58 



7-0 



760 



•95 



•74 



9-9 



83-7 



•04 



•58 



9-4 



772 



100 



•74 



5-9 



80-0 



•90 



•58 



8-4 



793 



•90 



•73 



6-7 



82-2 



•97 



•57 



91 



75 5 



•99 



•72 



5-5 



79-3 



•98 











Phil. Mag. S. 4. Vol. 32. No. 213. July 1866. 



F 



