62 'Different Kinds [Book t. 



ferencc of the pulley, and confequently always perpen- 

 dicular to the radius. The powers applied to pullies 

 aft more forcibly in proportion as their diftance from 

 the axis is greater, whether the cords rim in feveral 

 groves, or feveral pullies of different diameters turn 

 upon the fame axis ; thcfe powers therefore which 

 aft at the grtateft cliitance from the axis will have the 

 advantage over the other. Let IP, fnopofe a weight 

 of fix pounds to be placed at I (Plate 11. fig. i.) there 

 ought then to be fix pounds at H to iuibin it, be- 

 caufe the radii c d and c i are equal. But three 

 pounds placed at K will fuftain the lame weighr, be- 

 caufe the radius c 2 is double the radius c d- t and it 

 requires but two pounds in L, becaufe the radius c 3 

 is treble the nuiius c d. 



In all thefe cafes, the pulley performs the office of a 

 lever of the firit order, for it may be confidered as 

 an affemblage of fixed levers, of which the center is 

 the common fulcrum. All thefe levers have equal 

 arms in pullies with one gorge, and they are of un- 

 equal arms in pullies of feveral gorges. (See fig. i.) 

 All thefe pullies are fixed. 



It has been obfcrycd, that by means of a pulley of 

 many gorges (fig. i.) the actions of two unequal 

 powers may be rendered equal ; in the fame manner 

 an equilibrium or a conftant relation may be preferved 

 between two powers, the relative forces of which 

 continually change. A pulley may be ufed for this 

 pur^ofe, which, inllead of many concentric gorges, 

 has but one, but that in a fpiral form, which confe* 

 quently augments the diameter by degrees, according 

 to the proportion m which the excels of one of the 

 two forces augments. For example, let a pulley A 

 (fig. 2.) have its gorge hollowed in a fpiral form, of 

 which the hollow is feen at g ft b c> and the plain at 

 de 43 kt there be fixed in the center of this pulley a 



barrel 



