nd Tackle

—A combination of pul arranged in one case to form a block, (hence, “block and tackle”), to secure a multiplication of power. The upper or fixed block gives the mechanical advantage of application, and the lower or movable block, by multiplying the travel of the rope as compared with that of the weight, increases the power in proportionate ratio. Each movable pulley halving the power nece ary, with two sheaves the force nece ary is one-half of one-half, or one quarter. Briefly, the weight capable of being lifted is equal to the force multiplied by twice the number of sheaves in the lower block, or by the number of “runs” of rope around them, which is the same thing; the friction of the tackle having to be deducted.