[61] “Galileo, to whom was reserved the glory of preparing, long before, the way for the theory of Newton, by the discovery of the law to which the acceleration of heavy bodies is subjected, having let fall from a great height different balls of gold, of lead, of copper, or porphyry, with a ball of wax, observed that all these bodies employed nearly the same time in falling to the earth. The ball of wax, the only one that was sensibly retarded, was no more than four inches from the earth at the end of the fall of the other bodies. Galileo, considering that this difference was very far from being proportional to that of the weights, concluded that it depended solely on the resistance of the air. This conjecture has been since verified by direct experiments, consisting in letting fall from the top of a tube, within which the vacuum has been made the most perfect possible, bodies of different materials, such as lead, iron, wood, cork, feathers, wool, &c, and it has been found that none of these bodies will then permit of our perceiving any sensible difference in the duration of their fall. As to bodies which raise themselves in air, such as smoke, it is known that their ascension is occasioned by the circumstance of their being specifically lighter than air: they are with respect to this fluid, situated as a piece of cork is with respect to water, which when immersed in that water to a certain depth, and then left to itself, rises again to the surface. The vulgar regard all as being without gravity which rises instead of falling: whence Newton remarked that the weight of the vulgar was the excess of the absolute weight of a body above the weight of the air. The ascent of air-balloons in the midst of the air is well calculated to undeceive the partisans of this theory of bodies without heaviness.” Haüy’s Natural Philosophy, vol. i. p. 48. [62] To Otto Guericke, a burgo-master of Magdeburgh, we are indebted for the invention of the pneumatic machine, or air-pump. [63] The atmosphere presses equally on the whole surface of the water in the well, until the rod of the pump is moved; but, by forcing the rod down, the bucket compresses the air in the lower part of the pump tree, which being elastic, forces its way out of the tree through the valve; so that when the bucket is again raised, that part of the pump tree under the bucket is void of air; and the _weight of the atmosphere_, pressing on the body of water in the well, forces up a column of water to supply its place; the next stroke of the pump rod causes another column of water to rise; and as long as the bucket fits the pump tree close enough to produce a vacuum, a constant stream of water may be drawn from below. Parkes’s Chemical Catechism, pp. 47, 418.