Weighing-Machines have been described by us under the article Balance, in which article, however, we have omitted a notice of the annexed singular but simple and useful contrivance, the invention of Mr. Hawkins, of Fleet-street. It is called the hydraulic weighing-machine, and is chiefly designed for domestic use. a, in the annexed figure, denotes a cylindrical vessel made of tin and japanned, and partly filled with water; b is another cylinder of the same kind, but of less diameter, resting upon, or floating in the water contained in a; c is a graduated scale, with a glass tube running up the middle, fixed to the exterior cylinder; the bottom of this tube opens into the lower part of the cylinder, therefore the water always stands at the same level in both. e is a dish or scale, for holding the article to be weighed, the pressure on which causes the internal cylinder to sink lower, and raise the water higher between the two vessels, the level of which is indicated by the tube, and the weight at such level exhibited on the scale.
There is of course a liability to change, by a portion of the water evaporating: but, by leaving a weight in the scale when not in use, and pouring in of a small quantity of water occasionally to bring it to the level of the mark on the scale, an adjustment is easily made.