the poles, would be desolated by an

unceasing winter.

-Some say the sun

Was bid turn reins from th' equinoctial road
Up to the Tropic Crab; thence down amain
By Leo and the Virgin, and the Scales,
As deep as Capricorn, to bring in change
Of seasons to each clime: else had the spring
Perpetual smil'd on earth with vernant flowers,
Equal in days and nights, except to those
Beyond the polar circles: to them day
Had unbenighted shone, while the low sun,
To recompense his distance, in their sight
Had rounded still th' horizon.

PAR. LOST, BOOk x. 1. 672.

James. In what manner is this prevented?

Tutor. By the axis of the earth N s being inclined or sloped about 23

degrees and a half out of the perpen dicular, as it is described by Milton;

-He bid his angels turn askance

The poles of earth twice ten degrees and more From the sun's axle.

In this case you observe, that all the parallel circles, except the equator, are divided into two unequal parts, having a greater or less portion of their circumferences in the enlightened than in the dark hemisphere, according to their situation with respect to N the north, or s the south pole.

Charles. At what season of the year is the earth represented in this figure?

Tutor. At our summer season; for you observe that the parallel circles in the northern hemisphere have their greater parts enlightened, and

their smaller parts in the dark. If DL represent that circle of latitude on the globe in which Great Britain is situated, it is evident that about two-thirds of it is in the light, and only one-third in darkness.

You will remember, that parallels of latitude are supposed circles on the surface of the earth, and are shown by real circles on its representative, the terrestrial globe, drawn parallel to the equator.

James. Is that the reason why our days towards the middle of June are 16 hours long, and the nights but 8 hours.

Tutor. It is; and if you look to the parallel next beyond that marked DL, you will see a still greater disproportion between the day and night, and the parallel more north than his is entirely in the light.

Charles. Is it then all day there? Tutor. To the whole space between that and the pole it is continual day for some time, the duration of which is in proportion to its vicinity to the pole; and at the pole there is a permanent day-light for six months together.

James. And during that time it must I suppose be night to the people who live at the south pole?

Tutor. Yes; the figure shows that the south pole is in darkness; and you may observe, that to the inhabitants living in equal parallels of latitude, the one north and the other south, the length of the days to the one will be always equal to the length of the nights to the other.

Charles. What then shall we say to those who live at the equator, and consequently who have no latitude?

Tutor. To them the days and nights are always equal, and of course twelve hours each in length, and this is also evident from the figure; for in every position of the globe one half of the equator is in the light, and the other half in dark

ness.

James. If, then, the length of the days is the cause of the different seasons, there can be no variety in this respect, to those who live at the equator?

Tutor. You seem to forget that the change in the seasons depends upon the position of the earth with respect to the sun, that is, upon the perpendicularity with which the rays of light fall upon any particular part of the earth, as well as upon the length of days.

Charles. Indeed I did; but does