of such a high magnifying power in the investigation of certain classes of objects, all ordinary preparations are best seen under a power of 500 or 600 diameters. It would be utterly impossible to give our readers the slightest idea of the benefits conferred on the human race by this marvellous instrument. Suffice it to say, that no naturalist or surgeon ever attempts the most simple investigation into the structure of any body without the aid of the microscope. It has already shown us that a world of creatures exists which, although invisible to the eye of man, are possessed of wonderful forms, colour, and beauty of structure, and is daily adding to our knowledge in this direction. We can hardly submit any substances to this marvellous instrument without discovering animal or vegetable life of the most vivid character. A drop of scum from the surface of a stagnant pool is instantly seen to be peopled with animal and vegetable life, when submitted to microscopic examination. At one moment a rolling ball glistening like glass slowly revolves past our view; then a little fellow like a piece of spiral spring screws his way along, backing when he meets with an obstacle; or a shuttle-shaped vegetable, apparently made of glass, with green balls inside him, slowly works his way from side to side, or, possibly, a mad battledore-shaped being dashes past at an inconceivable rate.
As it is indispensable that the object should be well lighted, a concave mirror is placed below it to reflect the rays of light from a lamp or white cloud, through the object when it is transparent. When it is opaque, it is illuminated by the rays of light being concentrated upon it by means of a convex lens. The name microscope appears by common consent to be applied more particularly to the compound instrument, the epithet of magnifier or magnifying-glass being kept for simple
