I. LECT. over, it would be absurd to say that the greatest moun tain on earth has more halves, quarters, or tenth parts, than the smallest particle of matter has. We have many surprising instances of the smallness to which matter can be divided by art: of which the two following are very remarkable. 1. If a pound of silver be melted with a single grain of gold, the gold will be equally diffused througl--the whole silver ; so that, taking one grain from any part of the mass (in which there can be no more than the 5760th part of a grain of gold) and dissolving it in aqua fortis, the gold will fall to the bottom. 2. The gold beaters can extend a grain of gold into a leaf containing fifty square inches; and this leaf may be divided into 500000 visible parts. For an inch in length can be divided into 100 parts, every one of which will be visible to the bare eye: consequently a square inch can be divided into 10000 and 50 square inches into 500000. And if one of these parts be viewed with a microscope that magnifies the diameter of an object only 10 times, it will magnify the area 100 times ; and then the 100th part of a 500000th part of a grain (that is, the 50 millionth part) will be visible. Such leaves are commonly used in gilding; and they are so very thin, that if 124500 of them were laid upon one another, and pressed together, they would not exceed one inch in thickness. Yet all this is nothing in comparison of the lengths that nature goes in the division of matter. For Mr. Leewenhoek tells, us that there are more animals in the milt of a single cod-fish, than there are men upon the whole earth : and that, by comparing these animals in a microscope with grains of common sand, it appeared that one single grain is bigger than four millions of them. Now each animal must have a heart, arteries, veins, muscles, and nerves, otherwise it could neither live How inconceivably small then must the par nor move. I. ticles of their blood be, to circulate through the smallest LECT. ramifications and joinings of their arteries and veins. It has been found by calculation, that a particle of their blood must be as much smaller than a globe of the tenth part of an inch in diameter, as that globe is smaller than the whole earth; and yet if these particles be compared with the particles of light they will be found to exceed them as much in bulk as mountains do single grains of sand. For, the force of any body striking against an obstacle is directly in proportion to its quantity of matter multiplied into its velocity: and since the velocity of the particles of light is demonstrated to be at least a million times greater than the velocity of a cannon-ball, it is plain, that if a million of these particles were as big as a single grain of sand, we durst no more open our eyes to the light, that we durst expose them to sand shot pointblank from a cannon. a B E K L That matter is infinitely divisible, in a mathematical sense, is easy to be demonstrated. For let A B be the length of a particle to be divided ; and let it be touched Note 3. Some additional illustrations may readily be afforded of the chemical as well as the mechanical division of matter: — Thus, if we take a grain of copper, and dissolve it in diluted nitric acid (aquafortis and water) the smallest drop will readily coat the surface of a table knife with that metal. A nearly similar though a more simple mode of dividing a body by solution may also be employed. If a grain of cochineal or common blue, be mixed with three gallons of water, it will be found, that each drop of the fluid mixture will have imbibed a portion of the colouring matter equal to about one hundred and thirtythousandth part of a grain. Mica or talc affords some very wonderful instances of the mechanical division of matter. A biock of less than an inch in thickness, having been known to furnish more than one million distinct plates. Our author speaks of the amazing extension LECT. at opposite ends by the parallel lines CD and E N which suppose to be infinitely extended beyond D and N. Set off the equal divisions, BG, G H, HI, &c. on the line EN, towards the right hand from B; and take a point, as at R, any where towards the left hand from A, in the line CD: Then from this point, draw the right lines R G, RH, RI, &c. each of which will cut off a part from the particle A B. But after any finite number of such lines are drawn, there will still remain a part, as A P, at the top of the particle, which can never be cut off: because the lines DR and E F being parallel, no line can ever be drawn from the point R to any point of the line E F that will coincide with the line R D. Therefore the particle A B contains more than any finite number of parts. Attraction. Cohesion. A fifth property of matter is attraction, which seems rather to be infused than inherent. Of this there are four kinds, viz. cohesion, gravitation, magnetism, and electricity. The attraction of cohesion, is that by which the small parts of matter are made to stick and cohere together. Of this we have several instances; some of which follow. : 1. If a small glass tube open at both ends, be dipped in water, the water will rise up in the tube to a considerable height above its level in the basin which must be owing to the attraction of a ring of particles of the glass all around in the tube, immediately above those to which the water at any instant rises. And when it has risen so high, that the weight of the column balances the attraction of the tube, it rises no higher. This can be no of a single grain of gold by beating, but wonderful as this may appear, it can in no shape be compared with the micrometer wires lately drawn by Dr. Wollaston, which have been obtained as small as the thirty-thousandth part of an inch in diameter. Note 4. If a series of glass tubes, varying in size, be employed in. stead of the one here alluded to, the experiment will be materially improved, as it may be then experimentally shewn that the height of I. ways owing to the pressure of the air upon the water in LECT the basin; for as the tube is open at top, it is full of air above the water, which will press as much upon the water in the tube as the neighbouring air does upon any column of an equal diameter in the basin. Besides, if the same experiment be made in an exhausted receiver of the air-pump, there will be found no difference." 2. A piece of loaf-sugar will draw up a fluid, and a sponge will draw in water: and on the same principle sap ascends in trees. 3. If two drops of quicksilver be placed near each other, they will run together and become one large drop. 4. If two pieces of lead be scraped clean, and pressed together with a twist, they will attract each other so the column of water depends principally on the internal diameter of the tube. Glass canes, admirably adapted for the illustration of this fact, may be procured at the glass-houses for a few pence, and as they are seldom drawn of one size throughout, a single cane may be divided into short lengths for the purpose.-A very beautiful mathematical figure may also be formed, by connecting two plates of flat glass in such a way as to represent the two covers of a book partly opened; the edges being accurately in contact at the one side, whilst the opposite side of the plates are held asunder by a thin wedge. The plates thus united, should be placed erect in a shallow trough of coloured water, and in a few moments a curved line will be formed called an hyperbola. It may be proper to state, that the figure is more immediately formed, if an essential oil is substituted for the coloured water. Note 5. The ascent of fluids in capillary tubes, has been applied to the construction of a common filter, and the advantage it possesses over a downward filter, arises from the facility with which the sediment may be separated from the clear fluid, which in the ordinary mode of filtration tends to choke the apparatus. Note 6. A reference to the same cause will readily account for the spherical form assumed by drops of falling rain, as well as a variety of other meteorological phenomena: a popular poet has very beautifully remarked, that "That very law which moulds a tear, That law preserves the earth a sphere, 1. LECT. strongly, as to require a force much greater than their own weight to separate them. And this cannot be owing to the pressure of the air, for the same thing will hold in an exhausted receiver. 5. If two polished plates of marble or brass be put together, with a little oil between them, to fill up the pores in their surfaces, and prevent the lodgement of any air, they will cohere so strongly, even if suspended in an exhausted receiver, that the weight of the lower plate will not be able to separate it from the upper one. In putting these plates together, the one should be rubbed upon the other, as a joiner does two pieces of wood when he glues them. 6. If two pieces of cork, equal in weight, be put near cach other in a basin of water, they will move equally fast toward each other with an accelerated notion, until they meet : and then, if either of them be moved, it will draw the other after it. If two corks of unequal weights be placed near each other, they will approach with accelerated velocities inversely proportioned to their weights : that is, the lighter cork will move as much faster than the heavier, as the heavier exceeds the lighter in weight. This shews that the attraction of each cork is in direct proportion to its weight, or quantity of matter. This kind of attraction reaches but to a very small distance ; for, if two drops of quicksilver be rolled in dust, they will not run together, because the particles of dust keep them out of the sphere of each other's attraction.? Note 7. This experiment may be shewn more perfectly, if the seeds of lycopodium be employed; as the fluid rings, which really produce the effects described in the preceding paragraph are not in this case allowed to operate. The seed already alluded to may be strewed upon a table, and water poured over its surface, without wetting the wood beneath. |