Fuly 15, 1886] 
Independently of the foregoing demonstration, the fallacy of 
the volcanic hypothesis will be comprehended by its advocates 
on learning that the quantity of lava requisite to form the cir- 
and Wales to a depth of 125 feet.' 
Before proceeding further with our demonstration it will be | 
necessary to establish the maximum temperature which solar 
radiation is capable of imparting to the lunar surface. This 
temperature, of course, varies with the distance of the primary 
and its satellite from the sun. By means of an actinometer the 
bulb of whose thermometer receives an equal amount of radiant 
heat on opposite sides, I was enabled to determine with desirable 
accuracy, sixteen years ago, that, when the earth is in aphelion, 
solar radiation on the ecliptic imparts a maximum temperature 
of 67°:23F., and that the retardation of the radiant energy occa- 
Lira 
SAS 
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NATURE 
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<—/ 
249 
sioned by the want of perfect atmospheric diathermancy reaches 
0°207. Consequently the temperature produced by solar radia- 
ut u | tion at the boundary of the terrestrial atmosphere is 
cular walls of Tycho would cover the entire surface eof England | 
67-25% 1207) Glee ttuba, 
when the earth is in aphelion. Agreeably to observations during 
the winter solstice, compared with observations at midsummer, 
at equal zenith distance, the augmentation of solar intensity 
when the earth is in perihelion amounts to 5°°84 F. ; hence the 
temperature produced by solar radiation reaches 
81-11 + 5°84 = 86°95 F., 
when the rays enter our atmosphere during the winter solstice. 
It should be observed that on theoretical grounds the increase of 
temperature, when the earth is in perihelion, will be in the 
ie y 
i cay Ge 
( | h pie a 
i . 7 ag r 
i 4 Z pe na 
ie Lina 
Captain Ericsson's Pyrheliometer. 
inverse ratio of the dispersion of the solar rays ; hence, as the 
aphelion distance is to the perihelion distance as 218°1 to 21079, 
it will be seen that the temperature produced by solar radiation 
when‘the earth is in perihelion will be 
218°1? x 67°°2 BS 
°-86 F. 
210°9" th 
Adding 0°207 for retardation caused by imperfect atmospheric 
| temperature of the lunar surface when presented to the sun while 
diathermancy, solar intensity during the winter solstice will be 
71°86 x 1°207 = 86°73 F. 
Calculation™ based on odservation, as before stated, proves that 
the perihelion temperature is 86°'95, thus showing a trifling 
discrepancy between theory and observation. 
t Area of England and Wales, 58,320 square miles; contents of the walls 
re < 1382 
of Tycho, 1382 cubic miles; hence = = X 5280 = 125'12 feet. 
5e 32! 
Adopting 86°73 as correct, it will be found that the 
yearly mean temperature produced by solar radiation when the 
rays enter the earth’s atmosphere will be 
81°11 + 86°°73 
seh! ae lO 7) — 83°92 F., 
2 
while the temperature produced by the sun’s radiant heat is only 
81°11 during the summer solstice, as before shown. Hence the 
the earth is furthest from the luminary can only be augmented 
Sirk. 
The remarkable fact that the moderate heat produced by solar 
radiation is capable of increasing the temperature of bodies 
previously heated to a high degree demands consideration in 
connection with the subject under investigation ; also the nature 
of the device, before referred to, for ascertaining the temperature 
produced by solar radiation. The accompanying illustration 
