Ferguson's Lectures on Select Subjects in Mechanics, Hydrostatics, Hydraulics, Pneumatics, Optics, Geography, Astronomy, and Dialling Volume 2 - Tapa blanda

Reseña del editor

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1814 edition. Excerpt: ... The curves which must be employed in practice, should be curves drawn parallel to those formed by the preceding method, it the distance of the semi-diameter of the roller. Platb JB Fig. Q. we have a perspective view of a xu wheel furnished with two wipers formed in this manner. FC and LJT correspond with bC and r.4, in Figs. 6. and 4. The curves AnmC, and OPy correspond with DTcoC in Fig. 6. and MP with DhmB. The diagonal curve JllN corresponds with the diagonal curve DinC, and OM, the breadth of the wiper, with ran or rB, the versed sine of the arch JIB, in Fig. 4. The breadth OJM, however, should always be a little greater than the versed sine of the arch. through which the lever is to be raised, since MN is the path of the roller over the wipers surface. Having thus described the different methods of raising weights, whether perpendicularly or round a centre, with a uniform velocity and force: it would be unnecessary to apply the principles of construction to those machines.which are formed for the elevation, of weights. The practical mechanic can easily do this for himself. There is one case, however, which deserves peculiar attention, because the wipers, formed scientifically, will not produce the intended effect. This happens in the large sledgehammer which is employed in forges. In Fig. Fs-7-7. BC is a large hammer moved round A as a centre, by means of the wiper MW acting upon its extremity AC, or upon the roller R. The hammer must be tossed up with a sudden motion, so as to strike the elastic'oaken spring f, which, being compressed, drives back the hammer with great force upon the anvil D. Now, if spiral wipers, constructed according to the directions already given, are employed, the hammer will indeed be raised...