Surron—Injfluence of Water- Vapour upon Nocturnal Radiation. 27 
“35 inch, makes (apart from the accompanying humidity) abso- 
lutely no impression upon the rate of fall. 
By dividing all the dew-points into sets in order of magnitude, 
irrespective of the months in which they occur, we have the follow- 
ing results for the four years 1900-1903 :— 
Fall of Number 
Be cit BH Husa at Be ek Temperature, of 
8 p.m. 8-9 p.m. Clear Nights. 
Per cent. M. per H. . 
Under 35° 46 4-7 Log) 2738 
35°-39°°9 46 4°9 2°2 190 
40°—44°-9 45 5-2 2°3 116 
45°-49°-9 51 4-0 2°1 56 
50°-54°-9 60 3°3 2-0 38 
55 and over. 73 2-4 15 15 
Here again we find absolutely no trace of a fall of temperature 
depending upon the quantity of moisture present. But we do 
see plainly that the humidity and the fall of temperature vary 
together, even though the table has not been arranged with any 
reference to the saturation percentage. We see it still more 
plainly by dividing the observations into sets according to the 
magnitude of the relative humidity :— 
Eamamiey et | at | RAVel0CtY erature, | ot 
8 p.m. 8 p.m. 8-9 p.m. Clear Nights. 
‘ M. per H. 5 
Under 30 °/, 37°8 7:3 2°8 68 
3007) —39) ,, 87-7 5:8 25 123 
ON -—49) ,. 33°9 4-7 22 182 
Gye —=69),, 87-1 3°8 1:8 157 
G0, 69... 38-9 3:6 1°6 96 
70 ,, and over. 42-6 3°3 1°5 62 
