66 Lieut.-Colonel Strachey on the Action of 



Table {continued). 



1843. 





Fall of 





Tension of 



thermome- 





vapour. 



ter, 6b 40m 

 to 17h40m. 



6h 40m. 



inch. 







•93 



4-4 



85-2 



•93 



50 



85-2 



•92 



5-3 



85-8 



•90 



6-2 



85-1 



•88 



4-2 



84-9 



•85 



6-7 



85-5 



•81 



5-7 



83-0 



•75 



6-4 



81-6 



•72 



5-7 



775 



•71 



5-2 



80-2 



•70 



71 



81-0 



•70 



73 



79-8 



•69 



6-6 



76-9 



•68 



75 



77-8 



•67 



8-2 



78-6 



S®8 



Percentage 



of clear 



sky. 



•95 

 •91 

 •98 

 •93 

 •96 

 •96 

 •93 

 '96 

 •94 

 •98 

 •97 



100 

 •96 



100 



1842. 



•95 

 •94 

 •93 

 •89 

 •89 

 •71 

 •71 



50 



85-5 



4-9 



84-2 



5-6 



85-9 



5-8 



86-6 



65 



85-4 



62 



85-2 



87 



791 



8-2 



78-8 



100 



100 



1-00 

 1-00 



1842 (continued). 





Fall of 





Tension of 



thermome- 





vapour. 



ter, 6h 40m 

 to 17h 40m. 



6h 40m. 



inch. 







•70 



7°-5 



78-3 



•69 



8-2 



78-9 



•69 , 



9-1 



80-3 



•69 



9-5 



80-3 



•65 



10-6 



81-2 



•65 



120 



81-7 



•64 



9-4 



78-7 



•61 



11-6 



79-3 



•57 



9-3 



773 



Percentage 



of clear 



sky. 



100 

 •99 

 •99 

 •95 



1-00 

 •99 



100 

 •98 

 •97 



1841. 



•97 

 •93 

 •91 

 •91 

 •88 

 •86 

 •83 

 •71 

 •70 

 •66 

 •64 

 •64 

 •63 

 •58 



5-4 



840 



4-5 



84-0 



5-8 



84-5 



4-9 



84-1 



8-5 



87-0 



6-3 



84-7 



6-7 



82-7 



55 



77-8 



10-8 



84-7 



6-8 



76-5 



60 



75-4 



70 



76-5 



6-7 



76-2 



65 



74-8 



•91 

 •98 

 •91 

 •93 

 •91 

 •93 

 •92 

 •99 

 •98 

 •99 

 •97 

 •98 

 •97 

 1-00 



The general conclusion that the loss of heat by radiation from 

 the earth at night is directly affected in a very considerable de- 

 gree by the quantity of vapour in the air, seems to be unmis- 

 takeably indicated by these figures. It is necessary to be pre- 

 pared for considerable discrepancies in single observations; for 

 though it is no doubt true that the loss of heat at night on the 

 earth generally is essentially due to radiation into space, yet this 

 will not be exactly the case at any particular place. The air/ the 

 temperature of which was measured and noted in the Madras 

 observations, was of course in motion, and probably, or rather 

 certainly, had acquired its temperature as it came up from some 

 distant place to Madras. The observed fall of temperature, there- 

 fore, has reference to the average condition of the earth, and of 

 the sky over it, throughout the region traversed by the current. 

 There will have been variations of the heat of the earth's surface, 

 of the serenity of the sky, and of the quantity of vapour in sus- 



