Some of the things exhibited are well worth attention. There is Beaumont and Mayer's thermogenic engine! which heats water and generates steam without fuel or fire. As yet, its applicability to mechanical purposes is not apparent; but ways have been fonnd of turning it to account. It is kept fully employed in heating the chocolate sold in thousands of cups; this is without any breach of the law that prohibits fire within the building. And the Emperor ordered one to be sent to the Crimea, where, in case of the troops having to pass another winter, it would serve to heat soup, coffee, or water, whether fuel was to be had or not - no unimportant consideration during a campaign. It may supply heat to the cooking-galley of a ship, as, well as to the chocolate-establishment; and thus a source of danger from fire on shipboard may be avoided.

The construction is simple enough. A boiler is made, traversed by a conical tube of copper, 30 inches diameter at the top, 85 inches at the bottom, inside of which a cone of wood of the same shape is fitted, enveloped in a padding of hemp. An oil-vessel keeps the hemp continually lubricated, and the wooden cone is so contrived as to press steadily against the inside of the copper, and to rotate rapidly by means of a crank turned by hand or horse-power. The whole of the boiler outside of the copper cone is filled with water. Thus constructed, the machine, with 400 revolutions a minute, makes 400 litres* of water boil in about three hours by the mere effect of the friction of the oiled tow against the copper. When once the boiling-point is reached, it may be maintained for any length of time, or as long as the movement is continued. It is quite easy to keep the steam in the boiler at a pressure of two atmospheres, where, besides the uses above mentioned, it blows a whistle as lustily as any locomotive.

There is also the process for preserving vegetables, and another by which fresh meat may be kept perfectly sweet, for perhaps an unlimited time. There are legs of mutton, loins of veal, poultry, etc, in the Exposition, which were prepared three years ago, and are still as good as on the first day of their treatment, and show no signs of alteration. They have all the odor and appearance of meat recently killed, no taint or shrinking being perceptible. There are fruits, also, preserved in the same way - bunches of grapes, melons, apples, etc.; and vegetables, among which a cauliflower is as plump and bright with bloom as if but just brought from the garden. What renders the process the more remarkable is, that no pains are required to exclude air from the things preserved, a wire-screen alone being necessary to keep off flies and other insects. A three yean' trial may, perhaps, be considered decisive; and now there remains to see whether place or climate affect the result If not, the discovery - if such it be - may be regarded as one likely to prove highly beneficial. One of our most eminent savans was offered a leg of mutton on his departure from Paris, that he might convince his friends in England of the reality of the process for preservation.

What the process is, remains a secret; but we have heard whispered by a distinguished chemist that it consists in nothing more than brief immersion in very weak sulphuric acid. The acid, it is said, so coagulates the albumen, that a coat is formed on the surface of the joints, impervious to the air, and without affecting the flavor.

* A litre is about a quart.