_Mrs. B._ If the case will admit of your putting the end of the lever under the resisting body, no fastening will be required; as you will perceive, when a nail is drawn by means of a hammer, which, though bent, is a lever of the first kind; the handle being the longest arm, the point on which it rests, the fulcrum, and the distance from that to the part which holds the nail, the short arm. But let me hear, Caroline, whether you can explain the action of this instrument, which is composed of two levers united in one common fulcrum. _Caroline._ A pair of scissors! _Mrs. B._ You are surprised; but if you examine their construction, you will discover that it is the power of the lever, that assists us in cutting with scissors. _Caroline._ Yes; I now perceive that the point at which the two levers are screwed together, is the fulcrum; the power of the fingers is applied to the handles, and the article to be cut, is the resistance; therefore, the longer the handles, and the shorter the points of the scissors, the more easily you cut with them. _Emily._ That I have often observed, for when I cut paste-board or any hard substance, I always make use of that part of the scissors nearest the screw or rivet, and I now understand why it increases the power of cutting; but I confess that I never should have discovered scissors to have been double levers; and pray are not snuffers levers of a similar description? _Mrs. B._ Yes, and most kinds of pincers; the great power of which consists in the great relative length of the handles. Did you ever notice the swingle-tree of a carriage to which the horses are attached when drawing? _Emily._ O yes; this is a lever of the first kind, but the fulcrum being in the middle, the horses should draw with equal power, whatever may be their strength. _Mrs. B._ That is generally the case, but it is evident that by making one arm longer than the other, it might be adapted to horses of unequal strength. _Caroline._ And of what nature are the other two kinds of levers? _Mrs. B._ In levers of the second kind, the weight, instead of being at one end, is situated between the power and the fulcrum, (fig. 6.) _Caroline._ The weight and the fulcrum have here changed places; and what advantage is gained by this kind of lever? _Mrs. B._ In moving it, the velocity of the power must necessarily be greater than that of the weight, as it is more distant from the centre of the motion. Have you ever seen your brother move a snow-ball by means of a strong stick, when it became too heavy for him to move without assistance? _Caroline._ Oh yes; and this was a lever of the second kind, (fig. 7.) the end of the stick, which he thrusts under the ball, and which rests on the ground, becomes the fulcrum; the ball is the weight to be moved, and the power his hands, applied to the other end of the lever. In this instance there is a great difference in the length of the arms of the lever; for the weight is almost close to the fulcrum.