of the gold is contained in a single grain of the mass. The gold-beaters, whom you have seen at work in the shops in Long-Acre, can spread a grain of gold into a leaf containing fifty square inches, and this leaf may be readily divided into 500,000 parts, each of which is visible to the naked eye: and by the help of a microscope which magnifies the area or surface of the body 100 times, 100th part of each of these becomes visible, that is, the 50 millionth part of a grain of gold will be visible, or a single grain of that metal may be divided into fifty million of visible parts. But the gold which covers the silver wire used in making what is called gold lace, is spread over a much larger surface, yet it preserves, even if examined by a microscope, an uniform appearance. It has been calculated that one grain of gold under these circumstances would cover a surface of nearly thirty square yards. The natural divisions of matter are still more surprising. In odoriferous bodies, such as camphor, musk, and asafoetida, a wonderful subtilty of parts is perceived, for though they are perpetually filling a considerable space with odoriferous particles, yet these bodies lose but a very small part of their weight in a great length of time. Again, it is said by those who have examined the subject with the best glasses, and whose accuracy may be relied on, that there are more animals in the milt of a single cod-fish, than there are men on the whole earth, and that a single grain of sand is larger than four millions of these animals. Now if it be admitted that these little animals are possessed of organized parts, such as a heart, stomach, muscles, veins, arteries, &c. and that they are possessed of a complete system of circulating fluids, similar to what is found in larger animals, we seem to approach to an idea of the infinite divisibility of matter. It has indeed been calculated that a particle of blood of one of these animalcula is as much smaller than a globe one-tenth of an inch in diameter, as that globe is smaller than the whole earth. Nevertheless, if these particles be compared with the particles of light, it is probable, that they would be found to exceed them in bulk as much as mountains do single grains of sand: In thousand species of the insect kind! Lost to the naked eye, so wondrous small Were millions join'd, one grain of sand would cover all, A heart which drives the torrent through its veins; BAKER. I might enumerate many other instances of the same kind, but these, I doubt not, will be sufficient to convince you into what very minute parts matter is capable of being divided: and with these we will put an end to our present conversation. CONVERSATION III. Of the Attraction of Cohesion. Father. Well, my children, have you reflected upon what we last conversed about? Do you comprehend the several instances which I enumerated as examples of the minute division of matter? Emma. Indeed the examples which you gave us very much excited my wonder and admiration, and yet from the thinness of some leaf-gold which I once had, I can readily credit all you have said on that part of the subject. But I know not how to conceive of such small animals as you described; and I am still more at a loss how to imagine that animals so minute, should possess all the properties of the larger ones, such as a heart, veins, blood, &c. Father. I can, the next bright morning, by the help of my solar microscope, show you very distinctly, the circulation of the blood in a flea, which you may get from your little dog; and with better glasses than those of which I am possessed, the same appearance might be seen in animals still smaller than the flea, perhaps, even in those which are in themselves invisible to the naked eye. But we shall converse more at large on this matter, when we come to consider the subject of optics, and the construction and uses of the solar microscope. At present we will turn our thoughts to that principle in nature, which philosophers have agreed to call gravity or attraction. / Charles. If there be no more difficulties in philosophy than we met with in our last lecture, I do not fear but that we shall, in general, be able to understand it. Are there not, papa, several kinds of gravity? Father. Yes, there are; two of which it will be sufficient for our present purpose to describe; the one is the attraction of cohesion; the other that of gravitation. The attraction of cohesion is that power which keeps the parts of bodies. together when they touch, and prevents them from separating, or which inclines the parts of bodies to unite, when they are placed sufficiently near to each other. Charles. Is it then by the attraction of cohesion that the parts of this table, or of the penknife, are kept together? Father. The instances which you have selected are accurate, but you might have said the same of every other solid substance in the room, and it is in proportion to the different degrees of attraction with which different substances are affected, that some bodies are hard, others soft, tough, &c. A Philosopher in Holland, almost a century ago, took great pains in ascertaining the different degrees of cohesion, which belonged to various kinds of wood, metals, and many other substances. A short account of the experiments made by M. Musschenbroek, you will hereafter find in your own language, in the second edition of Dr. Enfield's Institutes of Natural Philosophy. Charles. You once showed me that two leaden bullets having a little scraped from the surfaces would stick together with great force; you called that, I believe, the attraction of cohesion? Father. I did some philosophers who have made this experiment with great attention and accuracy, assert, that if the flat surfaces, which are presented to one another, be but a quarter of an inch in diameter, scraped very smooth, and forcibly pressed together with a twist, a weight of a hundred pounds is frequently required to separate them. As it is by this kind of attraction that the parts of solid bodies are kept together, so when any substance is separated or broken, it is only |