44 W. Dennis on the Temperature of 
Art. V.—Remarks on the Temperature of the two extreme Seasons 
in the Temperate Zones as affected by the Vuriations in the Sun’s 
Distance and in its —_ Velocity in the Ecliptic; abridged 
. from a treatise on Astronomy, (in course of preparation,) by 
ILLIAM DENNIS, Philadelphia, Pa. 
THE eccentricity of the earth’s orbit being about ,';th of its 
mean distance from the sun, the whole variation in its distance, 
or the difference between its greatest and least distances, must 
be —_ oth of the mean: and from Kepler’s law for the equal 
description of areas by the radius vector of the earth (or other 
jleasiy it aves that the velocity of the earth’s motion in its 
orbit, or the consequent angular motion of the sun in the eclip- 
tic, varies inversely as the square of this distance. Then, since 
a numerical quantity ees by asmall fraction of itself has its 
square increa y (a little more than) the double of teat frac- 
tion, it is evident that as the distance varies by about 3 oth of its 
mean value, the variation in the velocity must be about ; ‘th of 
its mean 
Again, the amount of light and heat received from the sun in 
a given time, following the general law of influences emanating 
as from a centre, also varies inversely as the square of its distance, 
and therefore follows precisely the same law that governs the 
variation of the sun’s angular motion in the ecliptic. Hence we 
conclude, 
1. That the whole variation in the rate at which light and heat. 
are received from the sun, or in other words, the saul of 
rate at its greatest and least distances, amounts to about 7 
of the mean rate. 
at the amount of light and heat received from the sun 
while passing through a given are of the ecliptic is the same in 
every part of its annual course ; ; its greater distance in one part 
being exactly compensated by the longer time occupied in pass- 
ing through the supposed arc in that part; and vice versa. 
Now the present position of the line of apsides i is such that the 
perihelion or minimum distance of the earth from the sun occurs 
about the first of January, or near our winter solstice, and the 
aphelion or maximum distance about the first of July, or near 
our summer solstice; and as the solstices are the se points 
of the northern and southern portions of the ecliptic respect 
ively, it happens that nearly all that part of the ccliptio i in which 
_the sun is nearest the earth is passed over while the sun issouth 
of the.equator, and that part in which it is most remote, pps o 
is north of that line. But since the ecliptic is divided i the 
equinoctial into equal portions (or ares) it follows from the sec 
ond of the conclusions just stated, that the sun communicates to 
