of different muscles; and in a great variety of amusing and useful experiments. In academies, and private families, it may be erected in the place allotted for amusement, where it will furnish entertainment for many a vacant hour. When it has lost its novelty, the shaft may from time to time be taken down, and a swing may be suspended in its place. It may be constructed at the expense of five or six pounds; that which stands before our window was made. for less than three guineas, as we had many of the materials beside us for other purposes. *

Dec. 8, 1800.-" Scientific Dialogues" have just reached us; they seem well calculated to follow "Evenings at Home," as they contain a large quantity of accurate knowledge in a compendious form, and in clear and easy language. We had begun a book on a similar plan, which we are pleased to find is now become unnecessary: we shall therefore bound our humble labours to a small volume on the rudiments of science for young children.

* 1810-Since this was first published I have constructed a Panorganon on a small scale, and portable. It shall be sent to that useful work, "Nicholson's Journal."

CHAPTER XVIII.

CHEMISTRY.

IN the first attempts to teach chemistry to children, objects should be selected, the principal properties of which may be easily discriminated by the senses of touch, taste, or smell; and such terms should be employed as do not require accurate definition.

When a child has been caught in a shower of snow, he goes to the fire to warm and dry himself. After he has been before the fire for some time, instead of becoming dry, he finds that he is wetter than he was before; water drops from his hat and clothes, and the snow with which he was covered disappears. If you ask him what was become of the snow, and why he has become wetter, he cannot tell you. Give him a tea-cup full of snow, desire him to place it before the fire, he perceives that the snow melts, that it has become water. If he puts his finger into the water, he finds that it is

warmer than snow; he then perceives that the fire which warmed him, warmed likewise the snow which then became water; or, in other words, he discovers, that the heat which came from the fire goes into the snow and melts it: he thus acquires the idea of the dissolution of snow by heat.

If the cup, containing the water or melted snow, be taken from the fire, and put out of the window on a frosty day, he perceives, that in time the water grows colder, that a thin, brittle skin spreads over it, which grows thicker by degrees, till at length all the water becomes ice; and if the cup be again put before the fire, the ice returns to water. Thus he discovers, that by diminishing the heat of water it becomes ice; by adding heat to ice it becomes water.

A child watches the drops of melted sealing-wax as they fall upon paper. When he sees you stir the wax about, and perceives that what was formerly hard now becomes soft, and very hot, he will apply his former knowledge of the effects of heat upon ice or snow, and he will tell you that the heat of the candle melts the wax. By these means the principle of the liquefaction of bodies by

heat will be imprinted upon his memory; and you may now enlarge his idea of liquefaction.

When a lump of sugar is put into a dish of hot tea, a child sees that it becomes less and less, till at last it disappears. What has become of the sugar? your pupil will say, that it is melted by the heat of the tea; but if it be put into cold tea, or cold water, he will find that it dissolves, though more slowly. You should then show him some fine sand, some clay, and chalk, thrown into water, and he will perceive the difference between mechanical mixture or diffusion, and chemical mixture or solution. Chemical mixture, as that of salt in water, depends upon the attraction that subsists between the parts of the solid and fluid which are combined. Mechanical mixture is only the suspension of the parts of a solid in a fluid. When fine sand, chalk, or clay, are put into water, the water continues for some time turbid or muddy; but by degrees the sand, &c. falls to the bottom, and the water becomes clear. In the chemical mixture of salt and water there is no muddiness; the fluid is clear and transparent, even whilst it is stirred, and when it is

at rest there is no sediment, the salt being combined with the water; a new fluid substance is formed out of the two simple bodies salt and water, and though the parts of the salt which compose the mixture are not discernible to the eye, yet they are perceptible by the taste.

He

After he has observed the mixture, the child should be asked whether he knows any method by which he can separate the salt from the water. In the boiling of a kettle of water he has seen the steam which issues from the mouth of the vessel; he knows that the steam is formed by the heat from the fire, which joining with the water drives its parts farther asunder, and makes it take another form, that of vapour or steam. may apply this knowledge to the separation of the salt and water; he may turn the water into steam and the salt will be left in the vessel in a solid form. If, instead of evaporating the water, the boy had added a greater quantity of salt to the mixture, he would have seen, that after a certain time, the water would have dissolved no more of the salt; the superfluous salt would fall to the bottom of the vessel, as the sand had done;