Surron—Influence of Water- Vapour upon Nocturnal Radiation. 33 
during 1896 and 1897, the mean differences—(1) between the 
minimum radiation temperatures at heights of 3 inches and 
0 inches; and (2) between the minimum radiation tempera- 
tures at heights of 38 feet and 19 feet, compared with the 
absolute and relative humidities at 2 a.m. In both cases the 
thermometer nearest the ground reads the lower :— 
Dew-Point 
Relative 
at m3—Mo- M3g—M19- Humidity at m3—Mo. mM3g—119- 
2am. 2 a.m. 
z ° O° fo) (e) 
Under 25° 5-1 2°8 Under 40 °/, 5°7 1°5 
25°-29°-9 5:3 2°6 40°/,-49 ,, 5°6 1:8 
30°-34°°9 5°3 Dow 50,, -59 ,, 5:1 1:8 
35°-39°-9 5-2 2-1 OD op, ED) = 5-1 2-1 
40°44°-9 4-5 1:2 UO 55 =O 5 4:7 2-0 
45°-49°-9 4-8 1°3 80 ,, & over. 3°9 15 
50°-54°°9 4-2 0:9 
55 and over. 4°3 1-0 
An explanation of these last results is not likely to be simple, 
nor indeed does it strictly belong to the subject-matter of this 
paper. 
Probably radiation, convection, and conduction have each 
an equally important share in producing them; but beyond 
mentioning this, I venture no further comment. 
