Nature's Teachings: Human Invention Anticipated by Nature

by J. G. Wood

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. The muscle, which furnishes the power, contracts about an inch, and, so doing, moves the hand over some forty inches of space. It has been well stated that if a man is able to hold in his hand, and with extended arm, a weight of twenty-five pounds, the muscle must be exerting a power of forty times as great, i.e. about a thousand pounds.

There is little doubt that, in such Crushing Instruments as have been mentioned, the idea has been taken from the jaws of sundry animals. We know, for example, that with ourselves, if we desire to crack a walnut or a filbert in our teeth, we always put it as far back as possible, so as to make the leverage as powerful as possible. No one would ever dream of cracking a nut with his front teeth, an act which would be very much like that of trying to break a piece of coal by pinching it with the tongs.

The left-hand figure of the illustration represents part of the jaws of the Wolf-fish, or Sea-wolf, as it is sometimes called, and a very wonderful crushing machine it is. The Sea-wolf (Anarrhicas lupus), sometimes called the Sea-cat, or Swine-fish, is tolerably common on our coasts, and, as it sometimes attains a length of seven feet, and is proportionately stout and muscular, the power of its bite may be estimated. The fish in question feeds chiefly on crustacea and hard-shelled molluscs, and is therefore furnished with an apparatus which can crush their shells. Extremes meet. The Sea-anemones, which are mere films of animal matter, and can be torn in pieces with the finger and thumb, can seize, swallow, and digest a crab or an oyster in spite of the thick and strong shells in which they are enclosed. So can the Sea-wolf, and fishes of a similar character. But nothing intermediate can touch them, and it is curious to reflect that such opposite means should produce a similar effect.

On reference to the illustration, the reader will see how exact is the parallel between the Nut-crackers and the Sea-wolf’s jaws, both being worked on the same principle, and both being furnished with a series of projecting points, which are used for the purpose of preventing the escape of the object which is to be crushed. The terrible grasping power of the crocodile, the dolphin, and other predacious creatures can be explained on the same principle.

The Rolling-mill.

We now come to another variation of the Crushing Machine, i.e. that in which the motion is constant, and not intermittent, as is the case with those machines which have just been mentioned.