To varnish the edges of these covers, make circles of any liquid upon the glass slide, and perform any other “circular” work mentioned hereafter, the little instrument known as “Shadbolt’s turntable” is almost indispensable. It is made as follows:--At one end of a small piece of hard wood is fixed an iron pivot about one-eighth inch thick, projecting half an inch from the wood, which serves as a centre upon which a round brass table three inches in diameter revolves. On the surface of this are two springs, about one and a half inches apart, under which the slide is forced and so kept in position, whilst the central part is left open to be worked upon. The centre is marked, and two circles half an inch and one inch in diameter are usually deeply engraved upon the table to serve as guides in placing the slide, that the ring may be drawn in the right position. When the slide is placed upon the “table” underneath the springs, a camel-hair pencil is filled with the varnish, or other medium used, and applied to the surface of the glass; the table is then made to revolve, and a circle is consequently produced, the diameter of which it is easy to regulate. Many objects for the microscope may be seriously injured by allowing the fingers to touch them--many more are so minute that they cannot be removed in this way at all, and often it is necessary to take from a mass of small grains, as in sand, some particular particle. To accomplish this, there are two or three contrivances recommended: one by means of split bristles, many of which will readily be found in any shaving brush when it has been well used. The bristles when pressed upon any hard surface open, and when the pressure is removed close again with a spring; but the use of these is limited. Camel-hair pencils are of great service for this and many other purposes to the microscopist. In _very_ fine work they are sometimes required so small that all the hairs with the exception of one or two finer pointed ones are removed. A few of various sizes should always be kept on hand. Equally necessary are fine pointed needles. They are very readily put up for use by thrusting the “eye” end into a common penholder, so as to be firm. The points may be readily renewed, when injured, on a common whetstone; but when out of use they may be protected by being thrust into a piece of cork. Knives of various kinds are required in some branches of microscopic work, but these will be described where “dissection,” &c., is treated at some length, as also various forms of scissors. In the most simple objects, however, scissors of the usual kind are necessary. Two or three sizes should always be kept at hand, sharp and in good order.