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The Pressure of the Atmosphere.

Our drawing greatly resembles the advertisements of the cement manufacturers who boast their power to mend glass and porcelain "stronger than it was before." But it is not any kind of glue that we propose to use to fasten together plates and bottles, glasses and plates, or even bottles to each other. We shall simply make use of the pressure of the atmosphere, and the different achievements we describe are only variations on the classic experiments of the hemispheres of Magdeburg.

As we have no air-pump at our disposal, we cannot produce a perfect vacuum; but the vacuum at our disposal will prove sufficient for the tests we shall expect it to fulfil.

The glass and plate. Suspend a glass from the ceiling by means of a string and nail, and underneath it burn a bit of paper. The air will dilate with the heat, and, in cooling, will produce a partial vacuum in its interior. This will suffice to cause a porcelain plate to hang from the glass, provided you press it against the glass before the cooling of the air commences. You can prevent the introduction of the outer air by rubbing the platter well with warm suet.

The plate and bottle. The two bottles soldered. The rim of the neck of the bottle being weak, this experiment is not a very easy one. We shall, however, make the vacuum as perfect as possible; and all we have to do is to place our bottle to the spout of a boiling teakettle. As soon as the bottle is full of steam, having already greased its mouth, apply your plate, and, as soon as the refrigeration is complete, you will see, by lifting the plate, that the attachment of these two articles is not so very fickle.

The two bottles soldered together at their opposing bases, and the bottle glued to the plate in the same eccentric way, are even easier experiments; this time it is the obverse of the bottles that you leave a moment over the steam. I do not enter here into any complex calculations: suffice it to show, by a single example, that there is nothing in these achievements that need cause the least surprise. Let us only remember that in consequence of the weight of the atmosphere (supposing that it balances a column of mercury in the barometer of the height of 76 centimetres) the pressure exercised by the atmosphere on one square centimetre is one kilogram. Therefore, as the bottom of a bottle possesses, say, a superficies of 30 square centimetres, it would, were it a perfect vacuum, support a weight of 30 kilograms.