Friday, April 28, 2017

Hot Air Balloons

I've mentioned hot air balloons before on this blog but today I'm sharing the beginning of an excerpt that came out in 1822. The reason I'm posting this blog because of the science involved and the date of this publication. The 19th century is filled with science, which was built upon in the next century. The source of this excerpt is Elements of science and art: being a familiar introduction to...Vol. 1 pg 162. You can finish reading the excerpt here.

The air-balloon is a machine, consisting of a bag i filled with air, so light, that it, together with the bag, forms a mass which is specifically lighter than the common air of the atmosphere. A cubic foot of common air is found to weigh above 554> grains, and to be expanded by every degree of heat marked on Fahrenheit's thermometers, about l-50th part of the whole. By heating a quantity of air, therefore, to 200 degrees Fahr., you will just double its bulk, when the thermometer stands at 54 in the open air, and in the same proportion you will diminish its weight; and if such a quantity of this hot air be inclosed in a bag, that the excess of the weight of an equal bulk of common air, weighs more than the bag with the air contained in it, both the bag and the air will rise into the atmosphere, and continue to do so till they arrive at a place where the external air is naturally so much rarefied, that the weight becomes equal, and here the whole will float.

The power by which hot air is impelled upwards, may be shown by the following experiment. RolL up a sheet of paper in a conical form, and by thrusting a pin into it near the apex, prevent it from ur rolling. Fasten it then by its apex, under one of the scales of a balance, by means of a thread; and having properly counterpoised it by weights put into the opposite scale, apply the flame of a candle underneath, and you will instantly see the cone rise; and it will not be brought into equilibrium with the other, but by a much greater weight than those who have never seen the experiment would believe.

If the magnitude of a balloon be increased, its power of ascension, or the difference between the weight of the included air and an equal bulk of common air, will be augmented in the same proportion. For its thickness being supposed the same, it is as the surface it covers, or only as the square of the diameter. This is the reason why balloons cannot be made to ascend, if under a given magnitude, when composed of cloth, or materials of the same thickness.

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