Levers are of various kinds, according to the purposes lor which they are designed; and, being eminently serviceable for the lifting of weights, we have subjoined the following representation of a Crossbar-lever, which is particularly calculated for raising earth that abounds with great quantities of stones; though this machine is likewise applicable to other objects —It was invented by Mrs. Wynd-ham, of Petworth, in Sussex, on whom the Society for the Encouragement of Arts, etc. in 1796, conferred their silver medal.
A, is the lever.
B, an upright piece of wood, to be affixed to the lever; care being taken to place the side marked with this letter opposite to that marked A on the lever; by which means it inclines backwards, and thus increases the power.
C, is a cross-bar, being the hand by which the workmen exert their strength.
D, is another cross-bar, to be placed at the bottom, behind the upright piece of wood, on which the labourers are to stand, and through which the end of the lever passes. These additions are so constructed, that they may be occasionally fixed and removed ; because they are to be employed only, when the strength of the rock, or earth, requires an increase of power.
Should the rock be elevated so considerably above the ground, as to endanger the men by its fall, when the separation takes place, the lever may be reversed ; so that the labourers will stand upon the bar intended for the application of their hands, in common cases ; and thus all danger will be effectually prevented.
Various other levers have been contrived; but, as they relate to particular branches of mechanics, we shall only take notice of Mr. Snart's sliding lever, which he quaintly calls an alexippos; and which was also laid before the patriotic Society above-mentioned.— As various accidents happen to horses that frequently fall, while they are in the shafts ; and the present construction of carts, as well as other two-wheeled carriages, is especially unfavourable to the animal in such a situation, by preventing him from being speedily raised ; Mr. Snart has contrived a lever for the express purpose of relieving the unfortunate quadruped. He farther states, that it may occasionally be of service in loading carts, where the common length of those vehicles is not in proportion to the articles to be carried.
The contrivance is ingenious, and, notwithstanding its pedantic name, deserves to be more generally known: but, as we are not disposed to enter into particulars, the inquisitive reader will resort to the 18th vol.of the Transactions of the Society for the Encouragement of arts, etc. where this invention is fully described, and illustrated with an engraving.