There will be a great advantage in keeping the lamp clean, especially the burner and air tubes; the neglect of cleanliness in lamps is too common: a candlestick is generally cleaned every time it is used, so should a lamp; and if a candlestick is not to be objected to, because it does not give light after the candle is exhausted, so a lamp should not be thought ill of, if it does not give light when it wants oil or cotton; but this last has often happened, because the deficiency is less visible. The glass tubes are best cleaned with a piece of wash leather. If a fountain lamp be left partly filled with oil, it may be liable to overflow; this happens by the contraction of the air when cold, and its expansion by the warmth of a room, the rays of the sun, or the heat of the lamp when re-lighted: this accident may be effectually prevented by keeping the reservoir filled, the oil not being subject to expansion like air. On this account, those with a common reservoir are best adapted for microscopic purposes. TO EXAMINE OPAKE OBJECTS WITH THE LUCERNAL MICROSCOPE. The microscope is represented as mounted, and entirely ready for this purpose, in Fig. 1. Plate III. To render the use of this instrument easy, it is usually packed with as many of the parts together as possible; it occupies on this account rather more room, but is much less embarrassing to the observer, who has only three parts to put on after it is taken out of its box, namely, the guide for the eye, the stage, and the tube with its magnifier. But to be more particular, take out the wooden slide A, then lift out the cover and the grey glass from their respective grooves under the slide A. Put the end N of the guide for the eye L M N into its place, so that it may stand in the position which is represented in this figure. Place the socket, which is at the bottom of the opake stage, on the bar Q X T, so that the concave mirror o may be next the end D E of the wooden body. Screw the tubes P O into the end D E. The magnifier you intend to use is to be screwed on the end o of these tubes. The handle G b, or milled nut, Fig. 2, must be placed on the square end of the pinion a. Place the lamp lighted before the glass lump n, and the object you intend to examine between the spring plates of the stage, and the instrument is ready for use. In all microscopes, there are two circumstances which must be particularly attended to; the modification of the light, or the proper quantity to illuminate the object; secondly, the adjustment of the instrument to the focus of the glasses and the eye of the observer. In the use of the lucernal microscope there is a third circumstance, which is the regulation of the guide of the eye, each of which I shall consider by itself.