91 
the heat that it would receive if it were outside the atmosphere. 
Of the remaining 25 per cent one-half reaches this horizontal unit 
by way of the diffuse reflection from the sky, so that with the sun in 
the zenith the unit receives 0.875 of the original solar heat. For a 
point on the equator during twelve hours this would amount to 
0.875 x 126060 of the total possible if the sun were in the zenith. 
Using this as a basal datum, Aymonnet obtains the relative numbers 
given in the following table or the ratio of the heat actually received 
during one day to that which would have been received if the sun had 
stood for twelve hours in the zenith. Thus on June 20, at latitude 30°, 
the horizontal unit receives 0.347 of that corresponding to the ideal 
sun in the zenith all day, while at the north pole on the same day 
the horizontal unit received during twenty-four hours 0.328 of what it 
would had the sun stood in the zenith for twelve hours. In fact the 
amount of heat received by horizontal surfaces is nearly uniform for 
all latitudes for the days June 15-July 28. These relative numbers 
or ratios may be turned into absolute calories by multiplying them 
by the so-called “solar constant,’ whose value is probably between 
two and three calories per minute per square centimeter. 
Relative quantities of total heat received on specified days from the sun and sky 
at different latitudes by a unit surface of horizontal ground during one 
cloudless day, allowing for the absorption and diffuse reflection of ordinary 
clear air, as computed by Aymonnet. 
| Declin- Latitude— 
nation 7 = 
Mego: ofsun,| go | 10, | aoe. | so. | vo. | aoe. | om, 
Marcin a). sees ULE ee 007 | 0.301} 0.295 | 0.255] 0.175 | 0.075 0.029 0.000 
Mam ChigS ta teens a Ses cence se 3 02 . 298 297 . 268 - 190 . 098 . 049 O17 
Mri at MSS ARES 2 Fete 652| .295] .308| .284| .215| .127| .082| 058 
Prmrilel ester (ibe bee, ge 948| .292] .306] .296| .235| .157| .115 100 
Salt ae 1314} .288| .307] .310} .261] .191| .159| .151 
MOM ne ee as 1617 | .284| .305| .322] 281] .226| .207 205 
Marpineee Jot tii do Sis, 1854) .279| .304] 331] .208] .255| .249 250 
Mapenbnbiee nN aut oF 1 | 2058| .274| .304| .337| 318] .282] 280 286 
fins 5 2 eee 22 34] .272] .303| .342| .324] 304] 312 313 
Homesinet es sete 2320| .268} .302] .346] .329| .314| .328 326 
Tel to eae SEY a agar} .267| .301{ .347| .3390] .315] .325/  .328 
Sriete [Pe Teena 22 36| .272| .303| .342| 324] .304] 312] 314 
EjelbystoeeenOa vets Choa 7S _...| 2051] .274| .304| .3387| 313] .282/ 279 284 
TTT as ol 9 ee AO | 1850] .279] .304| .381| .208| .255| .249] 251 
ING aS AY Oe ge op el em | 1625] .284} .305] .822] .281| 226] .209 207 
JSESYEG IS Be Es a ape ee 1306] .288{ .307| .310} .261] .191| .159 152 
August 25 ___._- Set aig hee ae 1045| .200] 307} .301] .242] 164] .128 115 
Bupienther site. att Sos Om 648] .295| .303] .284] .215| 127] .o82] .058 
SentemiberIsi1/20 1222). isd! 300] .208| 207] .268] .190] .098| .049 O17 
=) September 23.0 ek eee 006) .301 295 | .255) .175] .075| 029 000 
