Mrs. B. Very probably it was so; for plate-glass has an extremely smooth, flat surface, admitting of the contact of a great number of particles, between two plates, laid one over the other.

Emily. But, Mrs. B., the cohesive attraction of some bodies is much greater than that of others; thus glue, gum, and paste, cohere with singular tenacity.

Mrs. B. That is owing to the peculiar chemical properties of those bodies, independently of their cohesive

attraction.

There are some other kinds of modifications of attraction peculiar to certain bodies; namely, that of magnetism, and of electricity; but we shall confine our attention merely to the attraction of cohesion and of gravity; the examination of the latter we shall resume at our next meeting.

CONVERSATION II.

ON THE ATTRACTION OF GRAVITY.

Attraction of Gravitation, continued-of Weight.-Of the fall of Bodies.-Of the Resistance of the Air.-Of the Ascent of Light Bodies.

EMILY.

I HAVE related to my sister Caroline all that you have taught me of natural philosophy, and she has been so much delighted by it, that she hopes you will have the goodness to admit her to your lessons.

Mrs. B. Very willingly; but I did not think you had any taste for studies of this nature, Caroline ?

Caroline. I confess, Mrs. B., that hitherto I had formed no very agreeable idea, either of philosophy, or philosophers; but what Emily has told me, has excited my curiosity so much, that I shall be highly pleased if you will allow me to become one of your pupils.

Mrs. B. I fear that I shall not find you so tractable a scholar as Emily; I know that you are much biassed in favour of your own opinions.

Caroline. Then you will have the greater merit in reforming them, Mrs. B.; and after all the wonders that Emily has related to me, I think I stand but little chance against you and your attractions.

Mrs. B. You will, I doubt not, advance a number of objections; but these I shall willingly admit, as they will be a means of elucidating the subject. Emily, do you recollect the names of the general properties of bodies ?

Emily. Impenetrability, extension, figure, divisibility, inertia, and attraction.

Mrs. B. Very well. You must remember that these are properties common to all bodies, and of which they cannot be deprived; all other properties of bodies are called accidental, because they depend on the relation or connection of one body to another.

Caroline. Yet surely, Mrs. B., there are other properties which are essential to bodies, besides those you have enumerated. Colour and weight, for instance, are common to all bodies, and do not arise from their connection with each other, but exist in the bodies themselves; these, therefore, cannot be accidental qualities ?

Mrs. B. I beg your pardon; these properties do not exist in bodies independently of their connection with other bodies.

Caroline. What! have bodies no weight? Does not this table weigh heavier than this book; and, if one thing weighs heavier than another, must there not be such a thing as weight?

Mrs. B. No doubt: but this property does not appear to be essential to bodies; it depends upon their connection with each other. Weight is an effect of the

power of attraction, without which the table and the book would have no weight whatever,

Emily. I think I understand you; is it not the attraction of gravity, which makes bodies heavy?

Mrs. B. You are right. I told you that the attraction of gravity was proportioned to the quantity of matter which bodies contained: now the earth consisting of a much greater quantity of matter than any body upon its surface, the force of its attraction must necessarily be greatest, and must draw every thing towards it; in consequence of which, bodies that are unsupported fall to the ground, whilst those that are supported press upon the object which prevents their fall, with a weight equal to the force with which they gravitate towards the earth.

Caroline. The same cause then which occasions the fall of bodies, produces also their weight. It was very dull in me not to understand this before, as it is the natural and necessary consequence of attraction; but the idea that bodies were not really heavy of themselves, appeared to me quite incomprehensible. But, Mrs. B., if attraction is a property essential to matter, weight must be so likewise; for how can one exist without the other ?

Mrs. B. Suppose there were but one body existing in universal space, what would its weight be ?

Caroline. That would depend upon its size; or, more accurately speaking, upon the quantity of matter it contained.

Emily. No, no; the body would have no weight whatever were its size; because nothing would attract it. Am I not right, Mrs. B. ?