P. 39.—To prepare sections of wood for slides there is a very simple instrument which may be made at home by any one possessed of a little ingenuity. Let a block of hard wood be selected, one and one-fourth inches square by two inches in length, its ends perfectly smooth. In one end drill a hole one-fourth of an inch in diameter, lengthwise, one and one-half inches. In the other end insert a common wood screw, its point filed square, until it reaches the hole. In the side of the block, one-half inch from the end in which the hole has been bored, insert another screw, with square point; this is to be used as a clamp. To cut the section take a branch the proper diameter, and which has been boiled in water, place it in the hole, and clamp solidly with the screw at the side. With a keen razor cut off the end even with the block. By turning the screw in the end of the block the branch will be pushed forward any distance desired, and the section can be cut by a sliding motion of the razor across the stem. The slices should be removed from the knife with a camel’s hair brush, slightly dampened, and may be preserved in weak spirits. The work is, of course, very delicate, and requires the skill and nicety of touch which only practice brings. To mount the sections in Canada balsam, as Dr. Wythe advises, the object should be placed exactly in the center of the slide, which must be carefully cleaned from dust, and a drop of the balsam placed upon it; hold the slide over a flame until the balsam spreads over the object. Air bubbles should be broken with a needle. A glass cover, warmed, should now be placed on the object and pressed sufficiently to remove the superfluous balsam. The whole should be put in a warm place until thoroughly dry. P. 42.—“Showers of blood,” or blood-rain. A shower of reddish dust mixed with rain, which has been known to fall in several places on the eastern coast of the Atlantic. P. 42.—“Diatoms.” “They are found in great abundance in the mud of rivers, lakes and ponds. They are also present in those deposits of clay which once formed the beds of rivers and lakes, and which are now dry. In order to procure the diatoms from these deposits, the earth or clay should be well washed with pure water, and the deposit allowed to settle and the water poured off. This may be repeated several times. The deposit is then to be washed with hydrochloric acid, and when the effervescence is over, the acid is poured off, and a fresh portion is added. This may be repeated several times. When no action occurs by its use cold, the deposit may be transferred to a watch-glass, and kept over a spirit lamp, at a temperature of about 200° for three or four hours. The deposit must then be well washed with pure water, and will be found to consist almost entirely of diatoms.”—_Lankester._