Before we begin to make observations, we should have a perfect knowledge of our microscope. There is no glass whatsoever but in which there are some spots, bubbles, threads, and other defects, which should be nicely inspected, in order that such appearances should not be represented as real and unknown objects: we must also endeavour to learn what effect the imperceptible dust has which adheres to the glasses of the microscope; a perfect knowledge of which may be acquired by observing the microscope several times.
To make proper observations, the sight, or focus, of the microscope must not precisely fall on the surface of the liquor, but a little above it; as not so much reliance should be placed on what passes upon the surface, as what is seen in the body of the liquor. There are often bubbles on the surface which have irregular motions produced by the contact of the air.
We can see much better with the light of two short candles, than in the brightest day, provided this light is not agitated, which is avoided by putting a small shade on the table, inclosing the three sides of the lights and the microscope.
It will often appear as though dark and opaque bodies become transparent, and even take different colours, or form concentrical and coloured rings, or a kind of rainbow on the surface; and other matters, which are seen at first sight transparent and clouded, become black and obscure; these changes are not real, but only depend on the obliquity the sight falls on the body with, and the height of the plain in which they are found.
When there are bodies in a liquor which seem to move with great swiftness, especially when they are on the surface, they form a furrowed motion in the liquor, which appears to follow the moving body, and which we might be inclined to mistake for a tail. This appearance deceived me at first, but I clearly perceived my error, when these little bodies met others which stopped them; for there was no longer any appearance of tails. These are the remarks which occurred during my experiments, and which I submit to those who would make use of the microscope for the observation of liquors.
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