Take a sufficient quant.i.ty of the flowers of pansies, or common violets, and after adding some water to them, strain the liquor through a cloth, and keep it in a bottle for use.

_A Sympathetic Ink which appears by being wetted with Water._

Mix alum with a sufficient quant.i.ty of lemon juice; then, if any letters or characters be written with this mixture, they will be invisible till they are wetted with water, which will make them appear of a grayish colour, and quite transparent.

Or, you may write with a strong solution of roch-alum only, and when the writing is dry, pour a small quant.i.ty of water over it, and it will appear of a white colour, like that of the paper before it was wetted.

Also all saline liquors, such as vitriolic, nitrous, and marine acids, diluted with water, the liquor of fixed vegetable alkalis, and even vinegar, will produce the same effect.

If a little aqua-fortis be mixed with the water, the writing will dry well, and not run out of its form when the paper is wetted.

_A curious Recreation with Sympathetic Ink, called the Book of Fate._

Make a book, consisting of seventy or eighty leaves, and in the cover at the end of it, let there be a case which opens next to the back, that it may not be perceived. At the top of each right-hand page, write any question you please; and at the beginning of the book, let there be a table of those questions, with the number of the pages in which each is to be found. Then write with common ink on separate papers, each about half the size of the pages, the same questions that are in the book; and under each of them, write the answer with the ink made with the litharge of lead, or the solution of bis.m.u.th.

Soak a double paper in the vivifying ink, made of quicklime and orpiment, or the liver of sulphur; and just before you make the experiment, place it in the case that is in the cover of the book.

Having done this, deliver some of the papers on which the questions are written, to the company; and after they have chosen such as they wish to have answered, let them put them into those leaves where the same questions are contained; then shutting the book for a few minutes, the sulphureous spirit, with which the paper in the cover of the book is impregnated, will penetrate the leaves, and make the answer visible, which will be of a brown colour, and more or less deep, in proportion to the time the book has been closed.

_A curious Recreation, called the Transcolorated Writing._

Write on a paper, with a violet-coloured liquor, as many letters or words as you please, and ask any person which he will choose to have the writing,--yellow, green, or red. When he has made his choice, have a sponge ready with three sides, which you can easily distinguish, and dip each of its sides in one of the three sympathetic inks; then draw the side of the sponge which corresponds to the colour the person has chosen, over the writing, once only, and it will directly change to the colour required.

_An Experiment with Sympathetic Ink, called the Oracular Letters._

Write on several slips of paper different questions, and such as may be answered by the name of some person: for example, Who is the merriest man in company?--_Answer_, Mr. * * *. To whom will Miss * * * be married?--_Answer_, To Mr. * * *. These questions are to be written in the sympathetic ink of the fourth cla.s.s, and exposed to the fire, and the answers written in the same ink, and left invisible. The papers are then to be folded in the form of letters, and in such a manner, that the part where the name is written shall be directly under the seal; in which case, the heat of the wax will make it visible. Then, if the letter be given to the person who requires the answer, he will find it plainly written.

_An Experiment with Sympathetic Ink, called Winter changed to Spring._

Take a print which represents winter, and trace over the trees, plants, and ground, with the green sympathetic ink; observing to make some parts deeper than others, according to their distance. When those parts are dry, paint the other objects in their natural colours; then put the print into a glazed frame, and cover the back of it with a paper, pasted over its border only. When this print is exposed to the heat of a moderate fire, or to the warm rays of the sun, all the gra.s.s and foliage will turn to a pleasing green; and if a yellow tint be given to some parts of the print, before the sympathetic ink be drawn over it, the green will be of different shades, and the scene, that a minute before represented Winter, will now be changed into Spring. When this print is placed in the cold, Winter will appear again, and be again driven away by the warm rays of the sun; and this alternate change of seasons may be repeated as often as you please, provided the print be not made too hot.

_A remarkable Experiment, called the Revivified Rose._

Take a rose that is quite faded, and throw in some common sulphur in a chafing-dish of hot coal. Hold the rose over the fumes, and it will become quite white; then dip it into a basin of water, and giving it to any one, tell him to put it into his box or drawer, and after locking it, to give you the key. About five or six hours afterwards, return him the key, and when he unlocks his drawer, instead of the white rose he put into it, he will find one perfectly red.

_How to Write on Gla.s.s by means of the Rays of the Sun._

Dissolve chalk in aqua-fortis, to the consistence of milk, and add to it a strong solution of silver; keep this liquor in a gla.s.s decanter, well stopped, and cutting out from a paper the letters you wish to appear, paste it on the decanter, and place it in the sun, in such a manner, that its rays may pa.s.s through the s.p.a.ces cut out of the paper, and fall on the surface of the liquor; then will that part of the gla.s.s through which the rays pa.s.s be turned black, while that under the paper will remain white; but particular care must be taken that the bottle be not moved during the time of the operation.

_To produce different Colours, by pouring a colourless Liquor into a clean Gla.s.s._

Take a strong solution of quicksilver, made with spirit of nitre; dilute it with water, and pour it into a hot gla.s.s, rinsed in strong spirit of sea-salt, and it will instantly become coloured. Or, if a solution of silver, made with spirit of nitre, considerably diluted, be poured into a gla.s.s, prepared in the manner above-mentioned, it will produce the same effect. And if you pour hot water upon new-made _crocus metallorum_, and put it into a clean gla.s.s, rinsed with any acid, it will produce an orange colour.

_To produce a Colour which appears and disappears by the Influence of the Air._

Put into a decanter some volatile spirit, in which you have dissolved copper filings, and you will have a fine blue tincture; and if the bottle be stopped, the colour will soon return again; and this experiment may be repeated a considerable number of times.

_To turn a colourless Liquor Black, by adding a White Powder to it._

Put a hot weak pellucid infusion of galls into a gla.s.s, and throw into it a grain of the vitriol of iron, calcined to whiteness, and considerably heated; then, as it falls to the bottom, it will make a black cloud, which will uniformly diffuse itself through the transparent liquor, and gradually turn it black.

The same effect may also be produced by the addition of a little vitriol of iron calcined to a yellow colour, or by the colcothar of vitriol calcined to redness.

The black liquor, produced as above, may be rendered pellucid again, by pouring the liquor hot into a gla.s.s rinsed with the pure acid of vitriol.

And to make this transparent liquor black again, pour to it as much hot oil of _tartar per deliquium_ as will saturate the acid, which has attracted the metallic matter.

_Freezing Mixture._

In the time of snow, a freezing mixture may easily be made, by mixing a little snow and common salt in a basin near the fire. If water in an iron cup or phial be put into this mixture, it will immediately be frozen; and if pounded ice and common salt be added, it will have a still more powerful effect.

_Experiments with the Microscope._

They who possess this amusing instrument, may easily perform with it a variety of pleasing experiments; among others, the following:--Leave some vinegar exposed in a saucer, for a few days, to the open air; then place a drop of it, by means of a clean pen, or a camel's hair brush, on the transparent object-plate of the microscope; and if the object-plate be properly illuminated from below, you will observe in this drop of liquor animals resembling some small eels, which are in continual motion.

If you slightly bruise some pepper-corns, and infuse them in water for a few days, and then expose a drop of it to the microscope, a number of animals of a different kind will be visible. These are of an oblong shape, and, like the others, in continual motion, going backwards and forwards in all directions, turning aside when they meet each other, or when their pa.s.sage is stopped by some obstacle.

In other infusions, as in that of new hay, differently shaped animalcules will be found. When the drop in which they swim, and which to them is like a pond, becomes diminished by evaporation, they gradually retire towards the middle, where they acc.u.mulate, and at length perish when entirely deprived of moisture. Previously to this, they appear in great distress, writhe their bodies, and endeavour to escape from that state of uneasiness which they evidently feel.

It the smallest quant.i.ty or drop of sulphuric acid be put into a drop of the infusion which swarms with these insects, they immediately throw themselves on their backs, and expire; sometimes losing their skin, which bursts, and suffers small particles of air to escape.

Those who wish to be furnished with microscopic eels, at all seasons, may have them in common paste, such as the bookbinders commonly use. It should neither be too stiff, nor too watery. Expose it to the air, and prevent its hardening or becoming mouldy on the surface, by beating it well together, when it has that tendency. After some days it will become sour; and then, if examined attentively by a microscope, mult.i.tudes of exceedingly small, long, and slender animalcules will be visible; these will grow larger, till they are of sufficient size to be seen by the naked eye. A drop or two of vinegar should now and then be poured on the paste; and sometimes, to prevent its being dry, a little vinegar and water. By this means microscopic eels may be had all the year. They must be applied to the microscope upon any flat surface, after having first put on it a very small drop of water for them to swim in. These are very entertaining objects when examined by any kind of microscope, but particularly the solar one, by which the motions of their intestines may very plainly be distinguished; and when the water is nearly dried away, and they are on the point of expiring, their mouths may be seen opening to a considerable width.

If some of the dust of the puff-ball be examined with the microscope, it appears to consist of perfectly round globules, of an orange colour, the diameter of which is only about the one-fiftieth part of the thickness of a hair, so that each of this grain is but the 1/125000th part of a globule, equal in diameter to the breadth of a hair.

The farina of flowers is found to be regularly or uniformly organized in each kind of plant. In the mallow, for example, each grain is an opaque ball, covered over with small points. The farina of the tulip, and of most of the liliaceous kind of flowers, bears a striking resemblance to the seeds of the cuc.u.mber: that of the poppy is like grains of barley.

There are certain plants, the leaves of which seem to be pierced with a mult.i.tude of small holes. Of this kind is the St. John's Wort. If a fragment of this be viewed with a good microscope, the supposed holes are found to be vesicles, contained in the thickness of the leaf, and covered with an exceedingly thin membrane; and these are thought to be the receptacles which contain the essential and aromatic oil peculiar to the plant. The view exhibited by those plants which have down, such as borage, nettles, &c. is exceedingly curious. When examined by a microscope, they appear to be covered with spikes. Those of borage are, for the most part, bent so as to form an elbow; and though really so close, they appear, by the microscope, to be at a considerable distance from each other. The entire appearance is very similar to that of the skin of a porcupine.

There are two kinds of sand, viz. the calcareous and the vitreous: the former, examined with a microscope, resembles large irregular fragments of rock; but the latter appears like so many rough diamonds. In some instances, the particles of sand seem to be highly polished and brilliant, like an a.s.semblage of diamonds, rubies, and emeralds.

Charcoal is a fine object for the microscope: it is found to be full of pores, regularly arranged, and pa.s.sing through its whole length.

Those who wish to observe the circulation of the blood, by means of the microscope, may readily obtain the desired satisfaction. An object employed chiefly for this purpose is the delicate transparent membrane which unites the toes of the frog; another object is the tail of the tadpole. If this membrane be extended, and fixed on a piece of gla.s.s illuminated below, the motion of the blood in the vessels will be distinctly visible; the appearance resembles a number of small islands, with a rapid current flowing between them.

Take a small tadpole, and, having wrapped its body in a piece of moist cloth, place its tail on the object-plate of the microscope, and enlighten it below, and you will see very distinctly the circulation of the blood; which in some of the vessels proceeds by a kind of undulation, and in others with a uniform motion. The former are thought to be the arteries in which the blood moves, in consequence of the alternate pulsation of the heart; the latter are said to be the veins. The circulation of the blood may be seen also in the legs and tails of shrimps. The transparent legs of small spiders, and those of bugs, will also afford the means of observing the circulation of the blood to very great advantage. The latter are said, by Mr. Baker, to exhibit an extraordinary vibration of the vessels, which he never saw any where else. Very small fish are good objects for this purpose; but the most curious of all spectacles of this kind, is that exhibited by the mosentery of a living frog, applied in particular to the solar microscope.