CRUSHING INSTRUMENTS

AS we are on the subject of leverage, we will take some examples of levers in Art and Nature, without, however, even attempting to exhaust the topic.

On the right hand of the illustration is shown a very familiar example of a lever, namely, nut-crackers, with a nut between them. This useful implement is simply an adaptation of levers of the second kind, the power being represented by the human hand, the weight by the nut, and the fulcrum being the joint of the instrument.

The common chaff-cutter, which is worked by hand, is another familiar example of this kind of lever, and so is the knife used by tobacconists in cutting cake Cavendish into threads, and by druggists for similar purposes. In these instruments the point of the knife is jointed to some fixed object, and becomes the fulcrum; the hand of the cutter supplies the power, and the weight is the object which is being cut. It will be seen that, by increasing the length of the handle, very great power can be obtained.

Exchanging the power for weight, we have in the common tongs, whether used for the coals or for sugar, a leverage of a similar character, the weight moving over a greater space than the power. A good example of this is to be found in the deltoid muscle of the human arm.