Page:Optics.djvu/148

 161. In the 18th volume of the Transactions of the Italian Society, there is a Memoir giving a detailed account of a catoptrical microscope, invented by Professor Amici, of Modena.

At one end of a tube inches long, and  in diameter, is placed a concave metallic speculum of a spheroidal form, having its foci at the distances  and  inches, respectively. The object to be examined is placed on a little shelf projecting from the stand, half an inch below the tube, and reduced to the nearer focus by a plain mirror, placed at half a right angle to the axis of the speculum, at the distance of inch from it. The image, formed in the farther focus, is viewed through a lens, which may be changed at pleasure, so as to increase or diminish the magnifying power, the object remaining unmoved, which gives this instrument a great advantage, in point of convenience, over the common compound refracting microscope.

In order to make the object sufficiently bright, there are attached to the instrument two concave mirrors, one of inches diameter, and  focus at the foot of the stand, and the other directly over the object, having an aperture in the center like that in the tube, to admit the rays to the plain mirror.

This instrument has a magnifying power of near a million, and is found extremely convenient from the horizontal position of the tube, which enables the observer to examine an object more at his ease, and for a longer time, than when stooping over a microscope of the common construction.

The Professor has contrived, by a very ingenious arrangement, to convert his instrument into a species of camera lucida, which enables him to draw any object on a magnified scale.

162. Here the office of the object-glass is executed by a pair of mirrors, , the former concave, the latter convex, having