Volume 2

Lectures on select subjects in mechanics, hydrostatics, hydraulics, pneumatics, optics, geography, astronomy, and dialling / By James Ferguson. With notes, and an additional volume, containing the most recent discoveries in the arts and sciences. By David Brewster.

  • Ferguson, James, 1710-1776.
Date:
1823
Catalogue details

Licence: Public Domain Mark

Credit: Lectures on select subjects in mechanics, hydrostatics, hydraulics, pneumatics, optics, geography, astronomy, and dialling / By James Ferguson. With notes, and an additional volume, containing the most recent discoveries in the arts and sciences. By David Brewster. Source: Wellcome Collection.

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    K H are tangents, in the points F and H. For this purpose, make G F and G H each equal to three feet, and raise the perpendiculars H /, F /, which will intersect one another in the point /, distant about 4 feet 9 inches and 4-10ths from the points F and H, and the centre of the arch F H will be deter- mined. The distance H K, through which the water runs be- fore it acts upon the wheel, should not be less than two or three feet, in order that the different portions of the fluid may have obtained a horizontal direction: and if H K be much larger, the velocity Gf the stream would be diminished by its friction on the bottom of the course. That no water may escape be- tween the bottom of the course K H and the extremities of the float-boards, K L should be about 3 inches, and the extremity o of the float-board n o should be beneath the line H K X, suf- ficient room being left between o and M for the play of the wheel, or K L M may be formed into the arch of a circle K M concentric with the wheel. The line L M V, called by M. Fabre the course of impulsion (le coursier (Timpulsion), should be prolonged, so as to support the water as long as it can act upon the float-boards, and should be about 9 inches distant from OP, a horizontal line passing through 0 the lowest point of the fall ; for if 0 L were much less than 9 inches, the water having spent the greater part of its force in impelling the float- boards, would accumulate below the wheel and retard its mo- tion. For the same reason, another course, which is called by M Fabre, the course of discharge (le coursier de decharge), should be connected with L M V, by the curve V AT, to preserve the remaining velocity of the water, which would otherwise be destroyed by falling perpendicularly from V to JV. The course of discharge is represented by FZ, sloping from the point O. It should be about 16 yards long, having an inch of declivity in every two yards. The canal whieja reconducts the water from the course of discharge to the river, should slope about 4 inches in the first 200 yards, 3 inches in the second 200 yards, de- creasing gradually till it terminates in the river. But if the river to which the water is conveyed should, when swoln by the rains, force the water back upon the wheel, the canal must have a greater declivity, in order to prevent this from taking place. Hence it will be evident, that very accurate levelling is necessary for the proper formation of the mill-course.