man knowledge, and affords to the mind inexhaustible materials for reflection. By what species of creatures are they inhabited? Does their proportion of light and heat agree with the constitution of such beings as inhabit our world-and if not such beings, of what kind are they? Are they more or less perfect than the bipeds who have the ascendancy on the earth? What events have occurred in their planets? Are lives proportioned to years as their years are shorter and longer than ours? Have they telescopes with which to view us as we view them? Have they any suspicion of our existence as we have of theirs? What are their habits, manners, religion, &c. &c.? In short, on this subject the imagination is bewildered though it is never wearied with the speculation!

Telescopes enable us to discern spots on these planets, by which we determine their period of rotation on their axes, some of which agree with ours, though others, as that of Jupiter, are much shorter. By displaying their moons it would also appear that they are nocturnal conveniences for beings who require them. In short, the whole displays the majesty, wisdom, and power, of the Creator, while the whole serves as a lesson to the vain glorious pride of man. To the inhabitants of Jupiter the earth is so near the sun as to be always invisible to eyes like ours; and Venus and Mercury, because still nearer, must also be unknown.

But however surprising are these considerations, they yield to another fact, that every star is doubtless a sun, and analogy leads us to conclude that these also are surrounded by their systems of planets like our own system; and hence we arrive at the overwhelming contemplation of millions of worlds like the globe on which we live, and equally adapted for existence, enjoyment, and happiness.

Nor is this all; for the stars themselves are not placed at random, or at equal distances, but they

are grouped or lie in shoals in space, every shoal or assemblage containing tens of thousands, perhaps millions, of stars shining by their own light, like our sun. Many faint spots, which to the naked eye appear like stars, prove on examination with telescopes to consist of a shoal or assemblage of myriads of stars, though so distant that the best telescopes do not enlarge them beyond the head of a pin. Nevertheless the fixed stars, and those of such shoals, must every one of them be millions of millions of miles asunder. How distant, therefore, must be shoals of them, which, when magnified a thousand times are but the size of the head of a pin!

Our sun belongs to a shoal, and all the small stars which we behold belong to this shoal, though tens of thousands may be counted with a telescope, and the milky way is rendered a gleam of light by their numbers; yet the nearest of these stars must be so distant, that a cannon ball would not reach it in seven millions of years! How vast, therefore, must be the shoal itself to which we belong -perhaps a cannon ball would not move from end to end in a million of million years-and yet this shoal at the distance of another shoal would be but a point, and appear like a single star!

I am lost in wonder as I write these paragraphs ; and well might Dr. Young exclaim, that "an undevout astronomer is mad."

LETTER LI.

Laws of Nature.

MY ESTEEMED CHILDREN.

How all these worlds are kept in order, how they move in mutual dependence, and how is preserved their system of continuous harmony, are questions

which naturally present themselves to your enquiring minds.

Some persons will tell you that they attract onę another; but this is absurd, for if attraction were not itself an absurdity, it is absurd to apply its powers to shoals of stars which, under such influence, would soon fall together and disorder every thing.

Attraction, or gravitation as some call it, is an absurdity, because nothing moves except in the direction in which some force from the opposite side is applied to produce the new position; and the motion is always in the direction of the force applied. Thus if you lay a ball on the table near your right hand, it will only move to the left by being pushed from the right towards the left, and the force must proceed from the right side. To make this plain try the experiment.

Well, then, if there are two balls, one to the left and another to the right, the left hand ball cannot make the right hand one move towards the left hand one, because the left hand one is not on the right hand side. So also with the left hand ball, considered with reference to the right hand ball. Lay two balls on the table, follow my reasoning, and determine for yourself.

No body, therefore, can attract another body universally, because the body said to attract is not on the side from which, in order to move it, the force must proceed. Miss A cannot attract Miss B, because Miss A is not on the other side of Miss B to push Miss B towards herself.

I have been particular in explaining this point, because this term attraction, is unthinkingly used in all books, and by teachers who follow books, and it is an absurdity which ought never to be‹mployed, for whenever bodies go together, or appear in some way to act upon one another, the special and particular cause ought to be investigated. There always is some cause, though invisible, and never

any attraction, which I have shewn to be a very gross absurdity. Others call it gravitation or weight, but a name explains no cause, and does but mystify us and leave us in ignorance, whilst it is from ignorance that we seek to be relieved.

The harmonious movements of the universe are produced by a more simple and intelligible cause. In my letter on the air in the school-room, I mentioned the fullness of the space, and all space is equally full; hence nothing can be moved without moving the gas in which it is placed, and this gas moves every thing around, according to a certain law of the distance. This law of motion in gas is also the law by which light, heat, odours, and sound, are propagated, and ought, therefore, once for all to be understood, while as it applics to so many things, you ought to understand it.

When you sit before a fire if you are one yard distant you have a certain degree of heat, but if you sit two yards off you have but a fourth of the heat, if at three yards but a ninth, or if at four yards but a sixteenth. So if you are reading at one foot from a candle you have a certain degree of light, and if two, three, and four feet off you have but a fourth, ninth, or sixteenth of the light which you had at one foot. The same is the case with sound, smell, and motion, or force, when propagated or extended through air or gas.

Now, then, you ought to know that the product of any number multiplied by itself is called the square of that number; thus 2 multiplied by 2 is 4, and 4 is the square of two; and 6 by 6 is 36, and 36 is the square of 6. This term is then applied to the above law; but as the cause is diminishing it is called inverse; and hence in the technical language of philosophers, light, heat, sound, odour, and motion in gas, are propagated, or spread, or scattered, inversely as the square of the distance; for in the preceding instances the numbers, 4, 9, and 16, are

respectively the squares of 2, 3, and 4 yards and feet.

The law itself arises from this circumstance, that as the air or gas receives the effect, larger surfaces are affected as the distances increase, consequently the original effect on any surface of the same size is lessened as the distance increases, by the general diffusion in a kind of spheres; and then the surfaces of spheres are to each other as the squares of their distances from their centres. A little consideration and a second reading will make this plain, if any difficulty arise.

You may now see how air propagates force, by laying two or three light pieces of paper on a table, and then by striking the table with your hand, you will see its force imparted to the papers; but the same experiment may be varied a hundred ways. Just so, then, and under this law, suns act through space filled with gas on planets, and planets on moons, moons on planets, and planets on one another; and this simple cause and its law, accord with all the phenomena of the solar system, explain every fact, and harmonize with every calculation and observation.

*****

LETTER LII.

Comets and other Celestial Phenomena.

MY ESTEEMED CHILDREN,

This astronomy, or philosophy of the stars and heavens, is an endless subject, and I must refer you to Squire, or to your Grammar of Philosophy, or the Wonders of the Heavens. I have already exceeded my limits, and I fear that I may weary you.

I should, however, like to say a few words about Comets, because whenever one appears, you have exhibited so lively an interest about it, and also