The Mercurial Shower.

Cement a piece of wood into the lower part of the neck of an open receiver, and pour mercury over it.— After a few strokes of the pump, the pressure of the air on the mercury will force it through the pores of the wood in form of a beautiful shower: which, if the receiver be clear and the weather be dry, will appear luminous in a dark chamber.

The Fountain in Vacuo.

Take a tall glass tube, hermetically sealed at the top and at bottom, by means of a brass cap, screwed on to a stop cock, and that to the plate of the pump. When all the air is exhausted the cock is turned, the tube is taken off the plate and immersed in a bason of mercury or water; then the cock being again turned, the fluid, by the pressure of the air, will play up in the tube, in form of a fountain, and afford a very pleasing appearance.

The Cemented Bladder.

Tie the neck of a bladder to a stop cock, which is to be screwed to the plate of the pump, and the air exhausted from the bladder; then turn the stop cock to prevent the re-entrance of the air, and unscrew the whole from the pump. The bladder will be transformed into two flat skins, so closely applied together, that the strongest man cannot raise them half an inch from each other; for an ordinary sized bladder, of six inches across the widest part, will have one side pressed upon the other with a force equal to 396 pounds weight,

Cork heavier than Lead.

Let a large piece of cork be pendent from one end of a balance beam, and a small piece of lead from the other; the lead should rather preponderate. If this apparatus is placed under a receiver on the pump,

you will find that when the air is exhausted, the lead, which seemed the heaviest body, will ascend, and the cork outweigh the lead. Restore the air, and the effect will cease. This phenomenon is only on account of the difference of the size in the two objects. The lead, which owes its heaviness to the operation of the air, yields to a lighter because a larger substance when deprived of its assistance.

The animated Bacchus.

Construct a figure of Bacchus, seated on a cask; let his belly be formed by a bladder, and let a tube proceed from his mouth to the cask. Fill this tube with coloured water or wine, then place the whole under the receiver. Exhaust the air, and the liquor will be thrown up into his mouth. While he is drinking his belly will expand.

The Artificial Balloon.

Take a bladder containing only a small quantity of air, and a piece of lead to it, sufficient to sink it, if immersed in water. Put this apparatus into a jar of water, and place the whole under a receiver. Then exhaust the air, and the bladder will expand, become a balloon lighter than the fluid in which it floats, and ascend, carrying the weight with it.

Experiment with a Viper.

Many natural philosophers, in their eagerness to display the powers of science, have overlooked one of the first duties of life-humanity; and, with this view, have tortured and killed many harmless animals, to exemplify the amazing effects of the air-pump. We will not stain the pages of this work by recommending any such species of cruelty, which, in many instances, can merely gratify curiosity; however, as many of our readers might like to read the effect on animals, we extract from the learned Boyle, an account of his experiment on a viper.

He took a newly-caught viper, and shutting it up in a small receiver, extracted the air. At first, upon the air's being drawn away, it began to swell: a short time after it gaped and opened its jaws; it then resumed its former lankness, and began to move up and down within the receiver, as if to seek for air. After a while it foamed a little, leaving the foam sticking to the inside of the glass; soon after, the body and neck became prodigiously swelled, and a blister appears on its back. Within an hour and a half from the time the receiver was exhausted, the distended viper moved, being yet alive, though its jaws remained quite stretched; its black tongue reached beyond the mouth, which had also become black in the inside. In this situation it continued for three hours; but on the air's being readmitted, the viper's mouth was presently closed, and soon after opened again; and these motions continued some time, as if there were still some remains of life.

It is thus with animals of every kind; even minute microscopical insects cannot live without air.

Experiments with Sparrows.

Count Morozzo placed successively several full grown sparrows under a glass receiver, inverted over water. It was filled with atmospheric air, and afterwards with vital air. He found,

First That in atmospheric air,

HOURS. MIN.

The water rose in the vessels eight lines during the life of the first; four during the life of the second; and the third produced no absorption.

Second-In vital air, or oxygen
The first sparrow lived

The second

The third
The fourth

HOURS, MIN.

5

23

2

10

The above experiments elicit the following conclusions:-1. That an animal will live longer in vital than in atmospheric air. 2. That one animal can live in air in which another has died. 3. That, independent of air, some respect must be had to the constitution of the animal; for the sixth lived 47 minutes, the fifth only thirty. 4. That there is either an absorption of air, or the production of a new kind of air, which is absorbed by the water as it rises.

OPTICS.

DEFINITIONS.

1. WHATEVER grants a passage to light is called

a medium.

2. By rays of light are understood its least parts, either successive in the same lines, or cotemporary in several lines.

It is clear that light consists of parts both successive and cotemporary, because in the same place you may stop that which comes one moment, and let pass that which comes immediately after: the least sensible part which may be stopped, or suffered to proceed, is called a ray of light.

3. Refrangibility is that disposition of a ray of light to be refracted, or turned out of its course, when it passes out of one medium into another.

When a ray of light passes out of a rarer medium into a condenser, Sir Isaac Newton supposes that it is refracted by the superior attraction of the denser medium, and by that means drawn out of its course.

4. Reflexibility is that disposition of a ray of light to be reflected or turned back into the same medium from any other medium upon whose surface it may fall.

Sir Isaac Newton supposes that light is reflected by impinging upon the solid parts of the body, but by some power of the body which is evenly diffused all over its surface, and by which it acts upon the ray, and impels it back without immediate contact.

5. Inflection is that disposition of a ray of light to be turned out of its course when it passes very near to the edges of bodies.