bly burn every thing belonging to the earth to atoms, were she similarly situated. The heat of the sun at Mercury, must be seven times greater than our summer heat;

-Mercury the first

Near ordering on the day, with speedy wheel
Flies swiftest on, inflaming where he comes,
With seven-fold splendour, all the azure road.

MALLET'S EXCURSION.

Charles. And do you imagine that, thus circumstanced, this planet can be inhabited?

Tutor. Not by such beings as we, are you and I could not long exist at the bottom of the sea; yet the sea is the habitation of millions of living creatures; why then may there not be inhabitants in Mercury, fitted for the enjoyment of the situation which that planet is calculated to afford? If there be not, we must be at a loss to know why such a body was formed; certainly it could not be intended for our benefit, for it is rarely even seen by us

Ask for what end the heavenly bodies shine?

Earth for whose use ? Pride answers, "'Tis for mine : -suns to light me rise,

My footstool earth, my canopy the skies."

Pore.

But do these worlds display their beams, or guide
Their orbs, to serve thy use, to please thy pride?
Thyself but dust, thy stature but a span,

A moment thy duration; foolish man!
As well may the minutest emmet say,
That Caucasus was raised to paye his way:
The snail, that Lebanon's extended wood

Was destined only for his walk and food :
The vilest cockle, gaping on the coast
That rounds the ample seas, as well may boast,
The craggy rock projects above the sky,
That he in safety at its foot may lie;

And the whole ocean's confluent waters swell,

Only to quench his thirst, or move and blanch his shell.

CONVERSATION XL.

PRIOR.

Of Venus,

Tutor. We now proceed to Venus, the second planet in the order of the solar system, but by far the most beautiful of them all :

Fairest of stars, last in the train of night,
If better thou belong not to the dawn,

Sure pledge of day, that crown'st the smiling morn
With thy bright circlet, praise him in thy sphere,
While day arises, that sweet hour of prime.

MILTON.

James. How far is Venus from the sun?

Tutor. That planet is sixty-eight millions of miles from the sun, and she finishes her journey in 224 days, consequently she must travel at the rate of 75,000 miles in an hour.

Charles. Venus is larger than Mercury, I dare say?

Tutor. Yes, she is nearly as large as the earth, which she resembles also in other respects,

her diameter being about 7700 miles in length, and she has a rotation about her axis in 23 hours and 20 minutes. The quantity of light and heat which she enjoys from the sun, must be double that which is experienced by the inhabitants of this globe.

James. Is there also a difference in her seasons, as there is here ?

Tutor. Yes, in a much more considerable degree. The axis of Venus inclines about 75 degrees, but that of the earth inclines only 23 degrees, and as the variety of the seasons in every planet depends on the degree of the inclination of its axis, it is evident that the seasons must vary more with Venus than with us.

Charles. Venus appears to us larger sometimes than at others.

Tutor. She does; and this, with other particulars, I will explain by means of a figure. Suppose s (Plate VII. Fig 17.) to be the sun, T the earth in her orbit, and a, b, c, d, e, f, Venus in her's now it is evident that when Venus is at a, between the sun and earth, she would, if visible, appear much larger than when she is at d in opposition.

James. That is because she is so much nearer in the former case than in the latter, being in the situation a, but 27 millions of miles from the earth T, but at d, she is 163 millions of miles off.

Tutor. Now as Venus passes from a, through b, c, to d, she may be observed by means of a

good telescope, to have all the same phases as the moon has in passing from new to full: therefore when she is at d she is full, and is seen among the fixed stars in the beginning of Cancer during her journey from d to e, she proceeds with a direct motion in her orbit, and at e she is seen in Leo, and will appear to an inhabitant of the earth, for a few days to be stationary, not seeming to change her place among the fixed stars, for she is coming towards the earth in a direct line but in passing from e to f, though still with a direct motion, yet to a spectator at T, her course will seem to be back again, or retrograde, for she will seem to have gone back from z to y; her path will appear retrograde till she gets to c, when she will again appear stationary, and afterwards from e to d, and from d to e, it will be direct among the fixed stars.

Charles. When is Venus an evening, and when a morning star?

Tutor. She is an evening star all the while she appears east of the sun, and a morning star while she is seen west of him;

Next Venus to the westward of the sun
Full orb'd her face, a golden plain of light
Circles her larger round. Fair morning star
That leads on dawning day to yonder world
The seat of Man.

MALLET'S EXCURSION,

When she is at a she will be invisible, her dark side being towards us, unless she be exactly

in the node, in which case she will suu's face like a little black spot.

pass over the James. Is that called the transit of Venus? Tutor. It is; and it happens twice only in about one hundred and twenty years. By this phenomenon astronomers have been enabled to ascertain with great accuracy the distance of the earth from the sun; and having obtained this, the distances of the other planets are easily found. By the two transits which happened in 1761, and 1769, it was clearly demonstrated, that the mean distance of the earth from the sun was between ninety-five and ninety-six millions of miles.

Charles. How do you find the distances of the other planets from the sun, by knowing that of the earth ?*

Tutor. I will endeavour to make this plain to you. Kepler, a great astronomer, discovered that all the planets are subject to one general law, which is, that the squares of their periodical times are proportional to the cubes of their distances from the sun.

James. What do you mean by the periodical times?

Tutor. I mean the times which the planets

The remainder of this conversation may be omitted by those young persons who are not ready in arithmetical operations. The author, however, knows from experience, that children may, at a very early age, be brought to understand these higher parts of arithmetic.