part BCD is that which the earth defcribes in the fummer, while the fun appears in the northern figns. The leffer part is DA B, which the carth defcribes in winter, while the fun appears in the fouthern figns. C the earth's aphelion, where it moves floweft, is in the greater part; A it's perìhelion, is in the leffer part, where the fun moves fastest.

There are, therefore, two reasons why our fummer is longer than our winter; firft, because the fun continues in the northern figns, while the earth is defcribing the greater part of it's orbit; and fecondly, becaufe the fun's apparent motion is flower while it appears in the northern figns, than whilft it appears in the fouthern

ones.

The fun's apparent diameter is greater in our winter than in fummer, because the earth is nearer to the fun when at A in the winter, than it is when at C in the fummer. The fun's apparent diameter, in winter, is 32 minutes, 47 feconds; in fummer, 31 minutes, 40 feconds.

But if the earth is farther from the fun in fummer than in winter, it may be afked, why our winters are fo much colder than our fummers. To this it may be anfwered, that our fummer is hotter than the winter, firft, on account of the greater height to which the fun rifes above our horizon in the fummer; fecondly, the greater length of the days. The fun is much higher at noon in fummer than in winter, and confequently, as it's rays in fummer are lefs oblique than in winter, more of them will fall upon the furface of the earth. In the fummer, the days are very long, and the nights very fhort; therefore the earth and air are heated by the fun in the daytime, more than they are cooled in the night;

and

and upon this account, the heat will keep increafing in the fummer, and for the fame reafon will decrease in winter, when the nights lengthen.

I fhould exceed the limits of a Lecture, if I were to inquire into the feveral concurring caufes of the temperatures that obtain in various climates; it may be fufficient, therefore, to obferve what a remarkable provifion is made in the world, and the feveral parts of it, to keep up a perpetual change in the degrees of heat and cold. Thefe two are antagonists, or as Lord Bacon calls them, the very hands of nature with which the chiefly worketh, the one expanding, the other contracting bodies, fo as to maintain an ofcillatory motion in all their parts; and fo ferviceable are thefe changes in the natural world, that they are promoted every year, every hour, every moment. From the oblique pofition of the ecliptic, the earth continually prefents a different face to the fun, and never receives his rays two days together in the fame direction. In the day and night, the differences are fo obvious, that they need not to be mentioned, though they are moft remarkable in those climates, where the fun at his fetting makes the greatest angle with the horizon. Every hour of the day, the heat varies with the fun's altitude, is altei ed by the interpofition of clouds, and the action of winds; and there is little room to doubt, but what the various changes that thus take place, concur in producing many of the fmaller and greater phenomena of nature.

Be this however as it may, it is certain that the various irregularities and intemperature of the elements, which feem to deftroy nature in one feafon, ferve to revive it in another: the immoderate heats of fummer, and the exceffive cold of winter,

prepare

prepare the beauties of the fpring, and the rich fruits of autumn. These viciffitudes, which feem to fuperficial minds the effects of a fortuitous concourfe of irregular caufes, are regulated according to weight and measure by that sOVEREIGN WISDOM, who weighs the earth as a grain of sand, the sea as a drop of water.

Our obfervations on the feafons cannot be better concluded than in the words of the excellent Hooker. Along and uninterrupted enjoyment of bleffings is apt to extinguish in us that gratitude towards the author of them, which it ought to cherifh and invigorate; the courfe of nature often glides on unobferved when there are no variations therein; and the fun himself shineth unnoticed, because he shineth every day. Since the time that GOD did first proclaim the edicts of his law, fays Hooker, heaven and earth have hearkened unto his voice, and their labour has been to do his will. But if nature fhould intermit her course, and leave altogether, though it were but for a while, the obfervation of her laws; if thofe principles and mother elements, whereof all things in this world are made, fhould lofe the qualities they now poffefs; if the frame of that heavenly arch erected over our heads fhould loofen and diffolve itfelf; if the celestial globes fhould forget their wonted motions, and by irregular volubility turn themfelves any way as it might happen; if the prince of the lights of heaven, which now as a giant doth run his unwearied course, should as it were through a languishing faintnefs begin to ftand and to reft himself; if the moon fhould wander from her beaten way, the times and feasons of the year blend themselves together by diforder and confufed mixture, the winds breathe out their last gafp, the clouds yield no rain, the earth be defeated of heavenly influence, and

her

her fruits pine away as children at the withered breafts of their mother, no longer able to yield them relief; what would become of man himself, whom all thofe things do now ferve? And how would he look back on thofe benefits, for which, when they were daily poured upon him in boundless profufion, he forgot to be thankful?

LECTURE

LECTURE XXXIX.

AN EXPLANATION OF THE PHENOMENA OF THE PLANETS, ACCORDING TO THE COPERNICAN SYSTEM.

I

SHALL here define again fome words which I have already explained, and recal your attention to fome circumftances which I have mentioned in a former Lecture. Thefe repetitions will not, I hope, be an object of complaint, as they will render this Lecture more perfect, and answer the beneficial purpose of grounding you more firmly in the fcience we are now treating.

The line that a planet describes round the fun is called it's orbit; the motion of all the planets in their orbits is from weft by the fouth to the caft; this is called their annual motion. .

The orbits of the planets are not all in the fame plane, but in planes inclined to each other, or interfecting each other at different angles. The orbit of the earth is taken as a ftandard, from whence their refpective inclinations are computed.

The planes of the feveral orbits of the plancts produced to the fixed ftars, mark the feveral circles which each planet would appear to defcribe in the fphere of the heaven to a fpectator placed in the fun; thefe circles may be called the heliocentric orbits of the planets.

The heliocentric orbit of the earth is the erliptic: to a fpectator in the fun, the earth will ap

pear