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A Journal of Natural Philosophy, Chemistry and the Arts, Svazek 31
Úplné zobrazení - 1812
A Journal of Natural Philosophy, Chemistry and the Arts, Svazek 22
Úplné zobrazení - 1809
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Strana 170 - ... stone. The hinder edge, as is evident from the construction, being capable of giving way to the resistance of the air, any degree of obliquity, for the purpose of a propelling power, may be used. I am...
Strana 86 - ... sail does not coincide with the centre of its surface, but is considerably in front of it. As the obliquity of the current decreases these centres approach and coincide when the current becomes perpendicular to the sail. Hence any heel of the machine backward or forward removes the centre of support behind or before the point of suspension...
Strana 85 - C be its centre of resistance, which experiment shows to be considerably more forward than the centre of the sail. Let CD be drawn perpendicular to AB, and let the centre of gravity of the machine be at any point in that line, as at D. Then, if it be projected in a horizontal path with velocity enough to support the weight, the machine will retain its relative position, like a bird in the act of skimming ; for, drawing CE perpendicular to the horizon, and DE parallel to it, the line CE will, at some...
Strana 86 - G, as a centre, and of being fixed in any position. The powers of the machine being previously balanced, if the least pressure be exerted by the current, either upon the upper or under surface of the rudder, according to the will of the aeronaut, it will cause the machine to rise or fall in its path, so long as the projectile or propelling force is continued with sufficient energy.
Strana 65 - Clay is particularly objectionable, as is also chalk, or calcareous earth of any sort. Sand is also not proper, unless accompanied with some binding quality : the bolder and coarser the sort of earth the better. When used, it should retain no more moisture than just to make it adhere together, under the pressure of the thumb and finger.
Strana 166 - Watt's steam horses ; and certainly more than twelve men can bestow upon their constant labour. If expansive first movers be made use of, they may be so constructed, as to be capable of doing more than their constant work; or their power may be made to accumulate for a few moments by the formation of a vacuum, or the condensation of air, so that these expedients may restore at one time, in addition to the working of the engine, that which they had previously absorbed from it.
Strana 87 - Even in this state, when any person ran forward in it, with his full speed, taking advantage of a gentle breeze in front, it would bear upward so strongly as scarcely to allow him to touch the ground ; and would frequently lift him up, and convey him several yards together.
Strana 166 - ... upon the principle of those birds which run themselves up. This action might be aided by making choice of a descending ground like the swift. With regard to another part of the first obstacle I have mentioned, viz. the absolute quantity of power demanded being so much greater at first than when the full velocity has been acquired; it may be observed, that, in the case of human muscular strength being made use of, a man can exert, for a few seconds, a surprising degree of force. He can run...
Strana 83 - The grand catastrophe in which this volcanic mountain [JorulIo] issued from the earth, and by which the face of a considerable extent of ground was totally altered, was perhaps one of the most extensive physical changes, that the history of our globe exhibits.
Strana 84 - ... form for producing a steady descent, the purpose for which they are intended. To render this subject more familiar, let us recollect, that in a boat, swimming upon water, its stability or stiffness depends, in general terms, upon the weight and distance from the centre of the section elevated above the water, by any given heel of the boat, on one side; and on the bulk, and its distance from the centre, which is immersed below the water, on the other side; the combined endeavour of the one to...