After fixing the object and getting the right focus, set the instrument horizontally, and arrange the light so that the object is well illuminated, and its lines quite clear and well defined. Now remove the cap of the eye-piece, and fix the camera-lucida in its stead. Lay a drawing-pad on the table under the camera-lucida, look through the square opening (or, if you use Mr. Beale's gla.s.s, look through the neutral gla.s.s), and you will see the object apparently projected on the paper. We say apparently, because in reality the image is not thrown on the paper at all, but on the camera, and the eye refers it to the paper, as being the nearest object. In fact, the principle on which this camera-lucida is arranged is exactly that of the Polytechnic ghost, which appears to be in one place, whereas it is in another.

Now take a pencil, cut it to a very fine point, and trace the outline of the object on the paper. At first you will think this to be an impracticable task, for the point of the pencil will totally vanish.

Soon, however, the eye will so adjust itself as to see the pencil and the object perfectly well, and by a little practice the observer will be able to sketch every object as rapidly and firmly as if he were copying a drawing, by means of tracing-paper. The neutral gla.s.s is perhaps to be preferred to the camera-lucida, as it is learned more easily, and gives less trouble than that instrument. Its cost is five shillings.

After you have practised yourself well in the handling of the microscope, your ambition will take another step, and lead you to the preparation of permanent objects. In order to set yourself up with the needful apparatus, you will have to disburse about five shillings. A small spirit-lamp will cost eighteenpence, and a small bottle of Canada balsam, another of asphalte varnish, and another of Dean's gelatine, will make about eighteenpence or two shillings more. A few pence will purchase a sheet or two of ornamental paper, and a few more a flat plate of bra.s.s or copper, about five inches by three. The rest of the five shillings may be expended in "slides" and thin gla.s.s, cut square.

Slides are merely slips of gla.s.s, three inches in length by one in width, and the thin gla.s.s is used for laying upon the objects and defending them from dust. We advise the square gla.s.s, because it scarcely costs one quarter as much as the round gla.s.s, and is equally effective when properly managed. There are several methods of "putting up" preparations--namely, dry, in Canada balsam, in gelatine, and in cells. We will take them in their order.

The simplest plan is, of course, the "dry" mode. Suppose that you want to preserve a tiny piece of down, or the scales from a b.u.t.terfly's wing.

First wash all the slides and gla.s.ses well, by dipping them into a strong solution of soda, and then into hot water, in order to get rid of grease, taking care never to touch them with the hand, but to take them out of the water with the forceps. This can be done at any time, and the gla.s.ses carefully wrapped up and placed in a box ready for use.

You now select one of the slides, and lay the object exactly in its centre. If very minute objects are used, they must be examined in order to see whether they are properly disposed. The next process is, to take one of the thin gla.s.ses with the microscope, and lay it very carefully over the object. Then cut a piece of ornamental paper, about two inches long and seven-eighths of an inch in width; cut or punch a circular piece out of its centre, damp it well, and cover the wrong side slightly, but completely, with paste. Lay it on the slide, so that the centre of the hole shall coincide with that of the object, work it down neatly with the fingers, and it will hold the square piece of thin gla.s.s, which is technically called the "cover," in its place. Watch it occasionally as it dries, and be ready to press down any part of the paper that may start up. Write, with ink, the name of the object on the end of the slide.

When you have made a dozen or two of these preparations, it will be time to letter and index them. On each slide paste a slip of white paper, and on the paper write a brief notice of the object, thus--

+---------------+ | SCALES. | | | | D. HEAD MOTH. | +---------------+

Then scratch with a bit of flint, or with a writing-diamond, if you have one, a number on the end of the slide, and have a note-book with a corresponding number opposite to which you enter the description at a fuller length, thus:--

18--Scales of Death's Head Moth (_Acherontia Atropos_), from centre of under-surface of right fore wing. Dry. June 4, 1864. +

The cross signifies that you prepared the object yourself, and the reason for adding the date is, that in after years you will have a valuable guide as to the durability of your preparations. If the specimen has been purchased or presented, always add the name of the seller or donor, as well as the date. These precautions may seem to be needlessly minute, but we have so often seen whole sets of valuable preparations rendered useless for want of ticketing, that we cannot too strongly impress on our readers the necessity for the note-book as well as the label, the one acting as a check upon the other. When the label has been affixed, and the details transferred to the note-book, the ink may be washed off the end of the slide.

There is another convenient method of putting up the elytra of beetles, parts of various insects, mosses, minute sh.e.l.ls, and similar objects.

Take a common pill-box of the smallest size, and cut a little cylinder of cork, that will nearly, but not quite, equal the height of the box, and fasten one end to the bottom of the box with glue. Now blacken the interior of the box and the cork cylinder. Put a little drop of Canada balsam, Arabian cement, or gum Arabic on the top of the cylinder; put the object on it, press it into its place, and, when the cement is hard, the preparation is complete. The cover of the box serves to keep the object from dust.

Now we come to the Canada balsam, a substance which produces beautiful effects when rightly handled, but is most aggravating to the learner, causing alternate irascibility and depression of spirits. Many objects, such as the antennae and feet of insects, will not show their full beauty unless they are mounted in Canada balsam. The method of doing so is as follows:--A week or two beforehand put the objects into ether or spirits of turpentine, and allow them to remain there until wanted. Pile up some old books, or take a couple of convenient wooden blocks; lay your bra.s.s plate upon them; light the spirit-lamp, and put it under the plate so as to heat it. Lay two or three slides on the plate, and all then can be heated at the same time.

Warm the bottle of Canada balsam, and with a gla.s.s rod take out a very little drop, and put it exactly in the middle of the slide. In order to insure this point, I always put a dot of ink on the wrong side of the slide. Stir it about with one of the needles mentioned on page 428, and if any bubbles rise, break them. When the balsam is quite soft and liquid, take one of the objects out of the bottle and put it into the balsam, exactly over the black dot. Now add a little more balsam, so as to cover it, and let it lie for a few moments. Take one of the gla.s.s covers, put a very little balsam on its centre, and lay it neatly over the object, pressing it down gradually and equally. Unless this be done, the object will not remain in the centre, but will shoot out on one side, and the whole operation must be begun _de novo_. Remove it from the hot plate and lay it on a cool surface, still continuing the pressure until the balsam has begun to harden. Lay a little leaden weight--a pistol-bullet partly flattened is excellent for the purpose--and on the cover write the name of the object, as already mentioned, and then proceed to prepare another slide.

Twenty such slides may be prepared in the course of a morning, and when they are finished they should be laid carefully in a cold place, where they will be free from dust. In a week or so the balsam will be quite hard, and then the slide may be completed. Take an old knife, which should be kept for this special purpose; heat the blade in the spirit-lamp, and then run it along the edges of the slide, so as to take off the superfluous balsam which has escaped from beneath the cover.

This must be done very quickly, or the balsam inside the cover will be heated by the knife, and the preparation spoiled. When this is done, cut the ornamental paper, as already described, number and label the slide, wash off the ink, and then the preparation is complete. Some objects are very troublesome to prepare, and require to be soaked in turpentine and boiled repeatedly in the balsam before they are completely penetrated with it.

Objects which are put up in Deane's gelatine are managed after a similar fashion, save that the gelatine is to be heated by placing the bottle in hot water, and that the turpentine is not needed. Vegetable structures show beautifully when thus prepared. To remove the superfluous gelatine use a _wet_ and not a hot knife.

Cells are very difficult to manage, and the novice had better not attempt to make them, but is hereby advised to purchase them ready made.

Suppose that the young microscopist has dissected the digestive organs of a bee, and wishes to preserve it in spirit; his best plan will be to use a cell for the purpose. Let him buy a cell of sufficient depth, float the preparation into it, fill it up with spirit, put the cover loosely on, and leave it for a week, occasionally raising the cover and stirring the preparation with a needle, in order to get rid of any air-bubbles that may have been entangled in the tissues.

Then let him wipe the edges of the cell very dry, put on a slight layer of gold-size or asphalte varnish--the former is preferable--fill up the cell a "b.u.mper," and lay the cover very gently upon it, beginning at one end and gently lowering it. With blotting-paper the liquid that escapes must be removed, the edges dried afresh, a flattened bullet placed on the cover, and with a very small camel's-hair brush the slightest possible coating of size painted round the edge of the cell. When it has hardened another may be given, and so on, until a thick hard wall of size has been built up round the edges and made the cover completely air-tight.

We presume that the reader does not intend to use his microscope merely as a toy, but that he desires to gain some insight into the works of Nature, and is therefore willing to set to work in a systematic manner.

It is now known that both animal and vegetable structures are built up by means of certain minute particles, technically called CELLS, and that in every part of a plant or of an animal can be recognised the const.i.tuents of which it is formed. We will, therefore, begin with the vegetables.

[Ill.u.s.tration: CELL, STRAWBERRY.]

Some of the lowest plants, such as the minute algae that inhabit the water, afford excellent examples of the simple vegetable cell; but as these plants are not readily procured by a beginner, we will select some familiar object wherein the cells may be found. If any soft and pulpy fruit be taken when it is quite ripe, and submitted to the microscope, the vegetable cell will be seen in a tolerably perfect form. The three rounded objects shown in the accompanying ill.u.s.tration are cells from the strawberry, specimens of which can easily be seen, if a very thin slice be cut with a razor or lancet, the latter being the preferable instrument. Be careful to dip the blade in water before cutting the fruit, and to float the slice from the blade to the gla.s.s slide by placing them both under water. Unless this precaution be taken, the section will not be flat, but will be crumpled up, and the cells will not be properly seen.

Within each of these cells may be seen a small rounded object, which is technically called the "nucleus;" and in some cases a smaller nucleus, called the "nucleolus," may be observed within the nucleus itself. The increase of cells mostly takes place by a process of division. A line pa.s.ses across the nucleus, which presently separates into two distinct parts, each of which recedes from the other, causing the cell to enlarge and alter its shape. Presently a line is seen across the cell itself, and in due time the cell is also divided into two parts, each having its own nucleus.

In the present instance the cell is totally spherical, because the fruit from which it was taken was soft, and allowed the const.i.tuent cells to expand. When, however, the vegetable substance becomes hard, the cells are pressed closely together, and their shapes are very much altered.

Sometimes, when the cells are of nearly the same size, and the pressure is equal on every side, the cells form regular twelve-sided figures, called "dodecahedra," which, when that occurs, show a six-sided outline.

A very thin slice of raw potato will show the twelve-sided cells beautifully, and has the further advantage of exhibiting the starch globules with which the cells are filled. Here is a figure of a potato cell, which presents a six-sided outline, just like that of a bee's waxen dwelling, and which is crowded with the beautiful globules of starch. If the reader likes to make a few dozen b.a.l.l.s of clay, and to squeeze them together in a ma.s.s, he will find that the central b.a.l.l.s will have lost their globular shape, and a.s.sumed a more or less regular twelve-sided form, very much like that of the potato cells.

[Ill.u.s.tration: CELL, POTATO.]

[Ill.u.s.tration: STELLATE TISSUE.]

Sometimes the cells run out longitudinally into cylinders, and attain the really enormous length of three inches; sometimes they become flattened, as the skin or epidermis of many plants; and oftentimes they push out their sides into arms or rays, like stars, and form the tissue which is technically called "stellate." Here is a specimen of stellate tissue taken from the pith of the common rush, wherein the rays are seen to be very regular: generally, however, the rays are extremely irregular, and require some little practice to detect them. Stellate tissue may be seen in the white portion of orange-peel, in the thick fleshy substance of many aquatic plants, in certain leaf-stalks, and in many similar objects.

We will now see how the soft cells which form the pulpy fruit of the strawberry can be changed into the hard timber of the oak or iron-wood tree.

[Ill.u.s.tration: RINGED STRUCTURE.]

Wherever a cell is destined to form part of a _permanent_ tissue, it is strengthened by receiving certain additions to its walls. These additions are technically known as "secondary deposit," and are made in various ways. Sometimes they extend in a thin layer over the whole cell-wall, leaving a number of little holes, which are called "pits,"

and earning the name of "pitted structures." Very frequently the secondary deposit is arranged in a series of rings, an example of which is given in the accompanying ill.u.s.tration. This object is taken from the mistletoe. Good examples of the ringed structures may be seen in the anthers of many plants, and in the leaf-stem of the common rhubarb, an example of which is shown in the next ill.u.s.tration. Another very common form of secondary deposit is the spiral, which is generally used where strength and elasticity are united. Two examples of the spiral form are given in the ill.u.s.tration; the first taken from the lily, and the second from the "rhizome," or subterranean stem of the water-lily.

[Ill.u.s.tration: RINGED AND SPIRAL STRUCTURES.]

Another beautiful form of secondary deposit is seen in the fern root. If the root be cut longitudinally, and the dark hard fibre dissolved carefully out with nitric acid, the deposit will seem to have a.s.sumed the shape of a winding staircase, and is then called "scalariform," or ladder-shaped. Similar structures may be found in asparagus.

[Ill.u.s.tration: WOOD-CELLS.]

The reader will see that the hardness of the structure depends entirely on the amount of secondary deposit, and we accordingly find that when the wood is hard and fit to be worked with tools the cells are almost wholly filled with the secondary deposit. In this state they are called "wood-cells." Examples of these cells may be seen in the accompanying ill.u.s.tration. In the first example, which is taken from the elder-tree, four cells are shown in order to display the manner in which their pointed ends are arranged. (The reader must remember that in all wood-cells the ends are pointed.) In the next example, which is taken from the chrysanthemum, the pitted structure is still retained; but in the last figure, which is drawn from the lime-tree, the entire cell is filled with secondary structure. The reader must understand that we can only give the veriest outline of the subject, and profess to do nothing more than indicate the method of observation, leaving the pupil to work out the details by himself.

[Ill.u.s.tration: HAIR OF LAVENDER.]

Another curious development of the plant-cells is the formation of HAIRS. These objects alone afford an inexhaustible field for the microscopist, and any one who chooses to work out the subject will find himself repaid if he makes a good series of preparations. In their primary forms the hairs are seen merely as little projections on the epidermis, whether of the stem, leaf, or petal, and by degrees a.s.sume their varied and beautiful forms. In order to show the singular forms which hairs sometimes a.s.sume, an ill.u.s.tration is here given of the hairs of the lavender leaf. This is one of the hairs that give the leaf its silvery gloss. It consists of an upright stem, from the top of which a number of forked branches shoot out horizontally, much like an open umbrella held upright. The object of this remarkable form is, that the delicate vessels in which the perfume is held should escape injury. If the reader will refer to the second figure, which represents a much magnified view of the edge of the leaf, he will see the globular perfume-gland standing under the shelter of the branching hairs.

The following plants afford valuable examples of hair:--Arabis, marvel of Peru, sowthistle, tobacco, southernwood, hollyhock, snapdragon, pansy (in throat of flower), deutzia (under-side of leaf), verbena, alyssum, tradescantia, borage, cowhage, and many others. The beautiful effect produced by the petals of flowers is caused by the imperfect hairs with which their surfaces are studded.

The POLLEN of plants is always worth observing, and some specimens are of remarkably beautiful shapes. Take that of althaea, crocus, cactus, heath, violet, daisy, lily, snowdrop, wallflower, willow-herb (a very beautiful form), hollyhock, periwinkle, primrose, &c. Put some up in Deane's gelatine, and dry some, besides examining them all when fresh.

The microscopist ought to examine the structures of WOOD by making sections in the directions transverse and longitudinal. A razor will answer very well for the purpose, and the wood should always be soaked inside, and the razor wetted before the section is made. It is often useful to make diagonal sections of several woods, especially those of the pine and juniper. All the forest trees should be examined, and their roots and bark should not be omitted. Cut sections of coconut-sh.e.l.l, vegetable ivory, sugar-cane (a most beautiful object when mounted opaque), bamboo, butcher's broom, &c.

MOSSES are beautiful objects, and can always be found. Examine particularly the fruit or seed-vessel, and note the structure of its different parts. Put these on a slide, and breathe on them, noting at the same time any change which may take place.

The SPORE CASES of ferns are extremely beautiful, and should be carefully examined. The little brown dots or streaks that are seen on the under surface of the fronds are called "sori," and contain a large but variable number of the sporanges. These consist of stalked sacs or cases, and differ much in shape, according to the species of fern. If the fern be fresh from which the sorus is taken, the sporanges may be seen writhing and twisting like so many serpents, and sometimes it happens that one of the sporanges bursts, and suddenly covers the field of the microscope with minute black dots. These dots are the spores or seeds of the fern, and when magnified with a very high power, they are seen to be variously shaped. One of the most remarkable spores is that of the equisetum, or mare's tail of the water. This spore looks like a ball with something coiled round it. As soon as the spore is discharged from its case, four threads are seen to uncoil themselves from around it, and by their elasticity to cause the spore to jump about as if alive. These fibres are technically named elasters, and are prolongations of the outer coat of the spore.

FUNGI of all kinds should be examined. There is never any difficulty in finding fungi, though the autumn is the best time of year for this purpose. "Mould," as it is popularly called, is a form a.s.sumed by many species of fungus, which, though objectionable to the careful housewife, are full of interest to the microscopist. The well-known mushroom and toadstools are the highest of the fungi. The black spots on leaves are fungi, mostly belonging to the genus puccinia, and the best specimens are generally found on the wild rose or bramble. The black "s.m.u.t" of wheat is another fungus, very pretty under the microscope, but very obnoxious to the farmer; and the "bunt" also belongs to the same vast tribe of plants, four thousand species of which are now known to exist.

The young observer should also look for the beautiful crystals which exist in many vegetable cells. The RAPHIDES, as these crystals are called, are of various forms, mostly shaped like curved needles, but often a.s.suming very pretty and regular outlines. Raphides are plentifully found in the bulb of the onion, in the rhubarb, the lily, the iris, &c. They are best mounted as opaque objects and, if the reader can procure a binocular microscope, he will see the form of the raphides better than with the single-tube instrument.

SEEDS of different plants should be carefully examined, especially those of small dimensions, which often exhibit some wonderful beauties of structure. The winged seed of various plants, such as the thistle, the dandelion, the valerian, and the willow-herb, are extremely interesting objects; while those of the yellow snapdragon, the mullein, the Robin Hood, and the bur-seed, are remarkably beautiful in form, though they have no parachute, as the feathery appendage is called.

Leaving dry land, we will devote a short time to the water. Let the reader take with him the simple collecting apparatus mentioned on page 430, and secure specimens of the water from different ponds, ditches, and streams. For collecting the larger objects a little net, which can be purchased cheap, is of very great use. It is easily made by any tinman, and if the young microscopist knows the use of solder, as all experimental philosophers ought to do, he can put it together in a few minutes. It is formed of a strip of zinc bent into the requisite form, and with a socket, to which a handle can be attached. A piece of coa.r.s.e muslin, or, rather, fine "net," is then stretched over the bottom, and the apparatus is complete.

In the water is sure to be found one of the lowest forms of vegetable life--namely, the "confervoid algae." Look for these in bright, clear pools, placing the collecting bottle near any greenish film collected around the stems of plants, or spread over the stones on the bed of the pool. If this film be very carefully taken up, it will produce many interesting forms of vegetable life. One of the most remarkable of these vegetables is that which is called "volvox globator," a figure of which is here given.