HYDRAULIC ARCHITECTURE, BOOK III.

808. One also uses the vacuum pump Original: "machine du vuide." This refers to the air pump used to evacuate air from a container. to determine the weight of a certain volume of air, in order to compare it to the weight of an equal volume that is more or less expanded. To do this, one takes a glass globe or a bottle, fits its neck tightly to the tube of the syringe to pump out the air—just as one empties the receiver—and after its spring The elastic pressure or tension of the air. has been weakened as much as possible, the tube is closed and separated from the syringe. The bottle is weighed in this state using very precise scales, after which the tube is opened to allow natural air to re-enter. The whole is then weighed a second time: the difference between the two weights gives the weight of the gross air Common atmospheric air as found at sea level. that was in the bottle. It is easy to determine the volume of this air by the weight of the quantity of water the bottle can contain (626). It was in this manner that Mr. Homberg found, through experiments conducted with great accuracy, that a cubic foot of air weighed 7 gros 9 grains in summer, and in winter 14 gros and about 19 grains; Historical French units of weight: a gros is roughly 3.8 grams, and a grain is about 0.05 grams. An ounce consisted of 8 gros. that is to say, a little more than one ounce and six gros, which is the same weight we found through the calculation of the barometer in article 792. Thus, one can conclude that in France, air in summer weighs only half of what it weighs in winter. Such a great difference comes, according to Mr. Homberg, from a greater movement of subtle matter A hypothetical fluid once thought to fill the spaces between particles of matter, facilitating heat and light. which produces a greater heat, and in summer separates the molecules of the air from one another, allowing them to expand their spring; whereas in winter, there being a smaller quantity of this matter spread through the air—or that which is there having less movement—the molecules move closer to one another, and consequently more of them are found in the same volume. Thus, air weighs more or less depending on the quantity of foreign matter with which it is charged; in great heat it is lighter because it contains more subtle matter, and in winter it weighs more because it contains much less. It follows from this reasoning and from article 807 that gunpowder must have much less force in summer than in winter, because it finds far fewer air particles to rarefy To make less dense; to expand., which is something I have proven in a great number of experiments.

However, the mercury of the barometer nonetheless remains elevated at 27 or 28 inches in one season as in the other, whereas it seems it should be elevated twice as high in winter as it is in summer. This is because the column of air pressing on the orifice of the barometer's vial is always, in its totality, of a weight nearly equal regardless of the season