On Rossetti’s Law of Cooling. 419 
From each of these we obtain, by Rossetti’s law (6), an equa- 
tion, viz.— 
S—a (6 +a) (0+ 460). (8) 
where S is the sun-heat, and 6 the mean temperature. 
The values of @ and a, deduced from these equations, taken 
in pairs, are— 
Lat a 
a 
80° 0-2489 
Lye ie ho 
(1) 70 ' (460)? 
70 0-3801 
ra 100-2 Refs ts 
60 4 0-4644 
3. (1 ae 
(3) 50 | Be (460)? 
50 0-4210 
rs t et ae ee 
(*) 40 > (460)? 
~, 40 * 0-3590 
; 114-3 Pid siete 
(5) 39 ¢ » “(4607 
.1ef0 00-3747 
Mean, 108°16° F. THEO? 
Pete 
~ 564,718 
This result would indicate for the temperature of the “ inclosure” 
of upper atmosphere that controls the radiation of heat at the 
earth’s surface, 108°16° F. below zero. 
Frélich,+ who has recently made important researches on this 
subject, with greatly improved and delicate instruments, at St. 
Petersburgh, has found a similar quantity, called by him Him- 
melstemperatur (Sky-temperature), which varies considerably 
from month to month and from night to night. Thus he found 
for the sky-temperature of the zenith, in 1876— 
20th October, 2 : . 123-70° F. below zero. 
21st : - 2 £1929 5 
23rd yg ; : : 93-19 > 
14th August, - - : 38-29 os 
15th =, : = - 39°00 “2 
ta : : - 49-09 “c 
14th October, » : : 34:33 —- 
* The latitudes below 30° give less reliable results, because the differences from which a 
and a are calculated are too small. 
+ Repertorium fiir Meteorologie, vol. vi., parti.,(p.1). (St. Petersburgh, 1876.) 
_ Scren. Proc., R.D.S. Vout w., PT. vi. 9Fr2 
