10

MANUFACTURES.

Sect. I.

III. INCREASE OF VELOCITY.

The fatigue produced on the muscles of the human frame does not altogether dependon the actual force exerted at each effort, but partly on the frequency with which it isexerted. The exertion necessary to accomplish every operation consists of twoparts: one of these is the propulsion of the Tool or instrument used; and the otheris the motion of some limb of the animal producing the action. If we take asan example the act of driving a nail into a piece of wood, one of these is, the propellingthe hammer head against the nail; the other is, raising the arm in order to lift thehammer. If the weight of the hammer is considerable, this latter part will cause thegreatest portion of the exertion. If the hammer is light, the exertion of raising the armwill produce the greatest part of the fatigue. It does therefore happen, that operationsrequiring very trifling force, if frequently repeated, will tire more effectually than morelaborious work. There is also a degree of rapidity beyond which the action of themuscles cannot be pressed.

It is of considerable importance for the economy of labour, to adjust the weight ofthat part of the animal’s body which is moved, the weight of the Tool it urges, andthe frequency of repetition of these efforts, so as to produce the greatest effect. Aninstance of the saving of time by making the same motion of the arm execute twoTags for operations instead of one, occurs in the simple Art of making the tags of boot-laces ;they consist, as is well known, of very thin, tinned, plate iron, and used to be cut out oflong strips of that material into pieces of such a breadth that when bent round theyjust enclosed the lace. Two pieces of steel have recently been fixed to the side of theshears, by which each piece of tin as soon as it is cut is bent into a semi-cylindricalform. The additional power required for this operation is almost insensible, and it isexecuted by the same motion of the arm which produces the cut. This work is usuallyperformed by women and children, and with the improved Tool more than three timesthe quantity is produced in a given time.* Whenever the work is itself light itbecomes necessary, in order to economise time, to increase the velocity. Twisting thefibres of wool by the fingers would be a most tedious operation: in the common spin-ning-wheel the velocity of the foot is moderate, but by a very simple contrivance thatof the thread is most rapid. A piece of cat-gut passing round a large wheel andthen round a small spindle effects this change. This contrivance is common to a mul-titude of Machines, some of them very simple. In large shops for the retail of ribandsit is necessary at short intervals to “ take stock,” that is, to measure and rewind everypiece of riband, an operation which, even with this mode of shortening it, is sufficientlytiresome, but which without it would be almost impossible from its expense. The smallballs of sewing cotton, so cheap and so beautifully wound, are formed by a machine onthe same principle, and but a few steps more complicated.

Manu-

factures.

* See Transactions of the Society of Arts , 1826.