Knight's cyclopædia of the industry of all nations, 1851 / [edited by George Dodd].

Date:
[1851]
Catalogue details

Licence: Public Domain Mark

Credit: Knight's cyclopædia of the industry of all nations, 1851 / [edited by George Dodd]. Source: Wellcome Collection.

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    AEEIAL BRIDGE. /E'SCULUS. 80 in 1844, for flasks intended to contain the aerated water, wlien required to keep it some time for further operations; or to transfer it to the common glass-bottles. It is an inge- nious piece of apparatus, strong enough to resist the expansive force of the gas, yet easily adjusted for the entrance or exit of liquids. AERIAL BRIDGE. [Bkidge.] AilRIAL WHEELS. This name has been given to a new form of wheel, in which the tire is made hoUow and very light. [Wheel.] AERO-DYNAMICS signifies the science which ti-eats of the motion of the air, or of the mechanical efiects of air put in motion. There are not many points in which this sci- ence bears directly on manufactuiing opera- tions or the arts generally ; but we may pre- sent a few considerations to shew its influence on moving machinery. As soon as we begin to move we feel, more or less, the resistance of the air. And, since any body in moving through a fluid, as au-, not only displaces a greater number of parti- cles of the fluid in equal times, in proportion as it moves faster, but causes each pailicle to react against the body more powerfully in pro- portion as the latter, by moving faster, strilies it with greater force ; it follows that the resist- ance of a fluid at rest against a body moving in it, or the resistance of the fluid in motion against a body at rest, varies ivith the square of the velocity of the body, or of the air; that is, if the velocity be suddenly made ten times as great, the resistance is made ten times ten, or a hundred times as great. And this is sufficiently near the truth for practical purposes when the velocities ai'e eight or nine hundred feet in a second. The resistance is nearly in the same pro- portion as the surface exposed, but a little gi'eater than this proportion on the larger surface ; that is, if we take two bodies of the same figure and material (two iron spheres for example), the surface of the second being twice that of the first, the resistance to the larger .sphere is a httle more than t-\^dce that to tlio smaller, the velocities being the same in both. The round ends and shai-p ends of solids sufler less resistance than the flat ends of the same. Thus, the sharp end or vertex of a cone is less resisted than the flat end or base. Two solids, similarly formed on the end to- wards the air, are not equally resisted unless tlie hinder parts arc also similar. If we suppose both the wind and the body to be in motion, the resistance is variously modified according to the direction of the motions of the two. If the wind and the body move in the same direction, with the same velocity, there is no resistance, for no air in displaced by the body. If the wud move 50 feet per second, and the body 100 feet, tho pressure on the body is tlie same as if it were at rest, v/ith acontravj/ynnd of 50 feet per second blowing on it. If the wind and the body- move in contrary directions, \nth velocities of 100 feet, the resistance is that of a wind of 200 feet per second ; and so on. The following table shows in pounds avoir- dupois, the pressure which different winds will exert upon a square foot of surface exposed directly against them. The first column is a rough representation of the second. Velocityof Wind. Force on the Miles Feet per second. square foot in Character of the per hour. pounds avoir- dupois wind. 1 1-47 •005 Hardly p creep ti ble. 2 2-93 •020 ) •044 1 3 4-40 Just perceptible 4 5 5-87 7-33 •079 •123 ^ I Gentle pleasant ■wind. 10 14-07 ■492 Pleasant brisk 15 22-00 1-107 1 gale. 20 29-34 1-908 25 30-07 3-075 1 Veiy brisk 30 44-01 4-429 35 51-34 6-027 High wind. 40 58-08 7-873 45 eo-oi 9-903 Very high. 50 73-35 12-300 Storm or tempest. 00 88-02 17-715 Great storm. 80 117-30 31-490 Huiricane. 100 146-70 49-200 Destructive hur- xicane. A few illustrations of the resistance and pressm-e of the air will bo met with under Aip.-GUN, Bellows, Blowing Machine, Sails, Windmill, <fec. AEROLITES, or Aih-stones, are masses of mineral substances which fall to the earth from the higher regions. As they do not bear very closely on the subject of the present work, a few details concerning them, under the heading Meteohic Stones, will suffice. AERONAUTICS, AEROSTATICS, AE- ROSTATION. The first of these three words IS compounded of two Greek words, which sig- nify literally the science or art of sailing in air; while the other two signify the staudiiiff of ladies in air. The Balloon, to which article we refer, is the most interesting ma- chine to which these studies relate. iE'SCULUS, or the Horse-Cliushmt, is a genus of plants winch subserves a few useful purposes. The popular name of/iorsf-che.stjiut