76 'The Ctiftlw. [Book I. 



It is eafy to perceive that the oipftan ads as a 

 perpetual lever of the firft or fecond order with un- 

 equal arms} an( i that the arm of refiftance is much 

 fhorter than that of the power. For the arm of the 

 lever by which the refiftance acls, is the radius of the 

 cylinder; and the arm of the lever bv which the 

 power acts, is the fame radius lengthened by the whole 

 extent of one of the crofs levers. 



Ships have often two kinds of capftans on board; 

 that is, a double Gapftan and a fmall one. The double 

 one is placed upon the firft deck, and rifes about four 

 or five feet above the fecond deck, it is dcfigned for 

 the more important purpofes, as to raife the anchor, 

 &c. The fmall capftan. is placed upon the fecond or 

 third deck between the main and mizen mafts, and 

 ferves to work. the fails, yards, &c. on different oc- 

 cafions. 



The crick or Jack is another machine by which a 

 great refiftance or weight may be overcome by a fmall 

 force. The fimple jack confifts of a bar of iron A B 

 (Plate IV. fig. i.) furnilhed with teeth in one of its 

 faces, and moveable in a cafe C E. The teeth of the 

 bar A B coincide with thofe of the nut D D, which 

 turns upon its axis by means of the handle M N. The 

 action then of the nut protrudes the bar, and confe- 

 quently raifes the weight placed at its head A. 



When the effort which each tooth of the nut makes 

 in D to raife the bar, is confide red as a weight ap- 

 plied to a lever, it is clear that the power applied to 

 the handle, is to that weight as the radius of the nut 

 is to the arm of the handle N M. Hence it may be 

 perceived, that by making the radius of the nut Very 

 fmall, in proportion to that of the handle, a very con- 

 fiderable weight may be raifed or moved by a mo- 

 Aerate force. A fmal] portable inftrument of this Kind 



is, 



