The microscope discovers legions of animalcules in mos liquors, as water, vinegar, beer, dew, etc. They are also found in rain, and several chalybeate waters, and in infusions of both animal and vegetable substances, as the seminal fluids of animals, pepper, oats, wheat, and other grain, tea, etc. etc. The contemplation of animalcules has rendered the term, infinitely small bodies, extremely familiar to us. A mite was anciently thought the limits of littleness; but we are not now surprised, to be told of animals twenty-seven millions of times smaller than a mite. Minute animals are found proportion-ably much stronger, more active and vivacious, than large ones. The spring of a flea in its leap, how vastly does it outskip any thing the larger animals are capable of! A mite, how vastly swifter does it run than a race-horse! M. De. L'Isle has given the computation of the velocity of a little creature, scarcely visible by its smallness; which he found to run three inches in half a second: supposing now its feet to be the fifteenth part of a line, it must make five hundred steps in the space of three inches; that is, it must shift its legs five hundred times in a second, or in the ordinary pulsation of an artery. The excessive minuteness of microscopical animalcules conceals them from the human eye. One of the wonders of modern philosophy is, to have invented means for bringing objects, to us so imperceptible, under our cognizance and inspection : creatures, a thousand times too little to be able to affect our sense, should seem to have been very safe; yet we have extended our views over animals, to whom these would be mountains. In reality, most of our microscopical animalcules are of so small a magnitude, that through a lens, whose focal distance is the tenth-part of an inch, they only appear as so many points; that is, their parts cannot be distinguished, so that they appear from the vertex of that lens under an angle not exceeding a minute.

If we investigate the magnitude of such an object, it will be found nearly equal to 3/100000th of an inch long. Supposing, therefore, these animalcules of a cubic figure, that is, of the same length, breadth, and thickness, their magnitude would be expressed by the cube of the fraction 3/100000. that is, by the number 27/1000,000,000,000,000 that is, so many parts of a cubic inch, is each animalcule equal to. Leuwenhoek calculates, that a thousand millions of animalcules, which are discovered in common water, are not altogether so large as a grain of sand. In the milt of a single cod-fish, there are more animals than there, are upon the whole earth; for a grain of sand is bigger than four millions of them. The white matter that sticks to the teeth also abounds with animalcules of various figures, to which vinegar is fatal; and it is known, that vinegar contains animalcules in the shape of eels. In short, according to this author, there is scarcely any thing which corrupts, without producing animalcules. Animalcules are said to be the cause of various disorders. The itch is known to be a disorder arising from the irritation of a species of animalcules found in the pustules of the body ; when the communication of it by contact from one to another is easily conceived, as also the reason of the cure being effected by cutaneous applications.

In the Philosophical Transactions, vol. 89, is a curious account of animalcules produced from an infusion of potatoes, and another of hemp-seed, by the late Mr. Ellis.

"On the 25th of May, 1768," he says, "Fahrenheit's thermometer 70°, I boiled a potato in the New-River water, till it was reduced to a mealy consistence: 1 put part of it, with an equal proportion of the boiling liquor, into a cylindrical glass vessel, that held something less than half a wine pint, and immediately covered it close with a glass cover. At the same time I sliced an unboiled potato, and, as near as I could judge, put the same quantity into a glass vessel of the same kind, with the same proportion of New-River water, not boiled; and, covering it with a glass cover, placed both vessels together. On the 26th of May, twenty-four hours afterwards, I examined a small drop of each by the first magnifier of Wilson's microscope, whose focal distance is reckoned 1/50th part of an inch; and, to my amazement, they were both full of animalcules, of a linear shape, very distinguishable, moving to and fro with great celerity, so that there appeared to be more particles of animal than vegetable life in each drop. This experiment I have repeatedly tried, and always found it to succeed in proportion to the heat of the circumambient air; so that even in winter, if the liquors are kept properly warm for two or three days, the experiment will succeed. I procured hemp-seed from different seedsmen, in different parts of the town; some of it I put into the New-River water, some into distilled water, and some into very hard pump-water: the result was, that in proportion to the heat of the weather, or warmth in which they were kept, there was an appearance of millions of minute animalcules in all the infusions; and, some time after, oval ones made their appearance, much larger than the first, which still continued; these wriggled to and fro in an undulatory motion, turning themselves round very quick all the time they moved forwards."