(277.) Two systems of pulleys, called _Spanish bartons_, having each two ropes, are represented in _fig. 123._ The tension of the rope P A B C in the first system is equal to the power; and therefore the parts B A and B C support a portion of the weight equal to twice the power. The rope E A supports the tensions of A P and A B; and therefore the tension of A E D is twice the power. Thus, the united tensions of the ropes which support the pulley B is four times the power, which is therefore the amount of the weight. In the second system, the rope P A D is stretched by the power. The rope A E B C acts against the united tensions A P and A D; and therefore the tension of A E or E B is twice the power. Thus, the weight acts against three tensions; two of which are equal to twice the power, and the remaining one is equal to the power. The weight is therefore equal to five times the power. A single rope may be so arranged with one moveable pulley as to support a weight equal to three times the power. In _fig. 124._ this arrangement is represented, where the numbers sufficiently indicate the tension of the rope, and the proportion of the weight and power. In _fig. 125._ another method of producing the same effect with two ropes is represented. (278.) If several single moveable pulleys be made successively to act upon each other, the effect is doubled by every additional pulley: such a system as this is represented in _fig. 126._ The tension of the first rope is equal to the power; the second rope acts against twice the tension of the first, and therefore it is stretched with a force equal to twice the power: the third rope acts against twice this tension, and therefore it is stretched with a force equal to four times the power, and so on. In the system represented in _fig. 126._ there are three ropes, and the weight is eight times the power. Another rope would render it sixteen times the power, and so on. In this system, it is obvious that the ropes will require to have different degrees of strength, since the tension to which they are subject increases in a double proportion from the power to the weight.