This opinion, however, was unfortunately to a great extent nullified by the statement which shortly afterwards appeared in his “Treatise on Astronomy,” and also in the “Outlines of Astronomy,” to the effect that the elliptic form of the earth’s orbit has but a very trifling influence in producing variation of temperature corresponding to the sun’s distance; the reason being that whatever may be the ellipticity of the orbit, it follows that equal amounts of heat are received from the sun in passing over equal angles round it, in whatever part of the ellipse those angles may be situated. Those angles will of course be described in unequal times, but the greater proximity of the sun exactly compensates for the more rapid description, and thus an equilibrium of heat is maintained. The sun, for example, is much nearer the earth when he is over the southern hemisphere than he is when over the northern; but the southern hemisphere does not on this account receive more heat than the northern; for, owing to the greater velocity of the earth when nearest the sun, the sun does not remain so long on the southern hemisphere as he does on the northern. These two effects so exactly counterbalance each other that, whatever be the extent of the eccentricity, the total amount of heat reaching both hemispheres is the same. And he considered that this beautiful compensating principle would protect the climate of our globe from being seriously affected by an increase in the eccentricity of its orbit, unless the extent of that increase was very great. “Were it not,” he says, “for this, the eccentricity of the orbit would materially influence the transition of seasons. The fluctuation of distance amounts to nearly 1/30th of its mean quantity, and consequently the fluctuation in the sun’s direct heating power to double this, or 1/15th of the whole. Now the perihelion of the orbit is situated nearly at the place of the northern winter solstice; so that, were it not for the compensation we have just described, the effect would be to exaggerate the difference of summer and winter in the southern hemisphere, and to moderate it in the northern; thus producing a more violent alternation of climate in the one hemisphere, and an approach to perpetual spring in the other. As it is, however, no such inequality subsists, but an equal and impartial distribution of heat and light is accorded to both.”[8] Herschel’s opinion was shortly afterwards adopted and advocated by Arago[9] and by Humboldt.[10] Arago, for example, states that so little is the climate of our globe affected by the eccentricity of its orbit, that even were the orbit to become as eccentric as that of the planet Pallas (that is, as great as 0·24), “still this would not alter in any appreciable manner the mean thermometrical state of the globe.”