SPEEDY ELEVATOR. 



5*1 



of E B, and lift the pier D. Thus wliile 1> B are wound 

 up from the bale to the height of the pulleys of A A, D 

 rifes treble that height ; and however great may be the 

 number of moving pieces, it multiplies the celerity and 

 acquired elevation of the uppennofl; by that of the firfi:. 



As the duration and celerity of all the movements is 

 the fame, the lengths of all the cords below the refpedlvc 

 pulleys mufi: be equal. 



As the whole acquired elevation is by thofe parts of the 

 piers which are drawn out of their folds, thefe ought to 

 have a very great propoition. Therefore B B reach the 

 bafe when down; and the heads of A A are but long 

 enough to keep them fafe m their grooves, when drawn 

 up. Again, as the ends of the cords bb will be above the 

 bafe according to the length of the heads of A A, the 

 heads of B B are fhortened, and the bodies of C C are pro- 

 longed below thofe ends, in order to fave room, and yet 

 afford thefe piers a fecure depth in the grooves of BB, 

 when drawn up. On the lame principle the heads of C C 

 are fhortened, and a part of D left under the ends of c c. 

 As thefe additions of faid pairs cannot increafe the eleva- 

 tion, the cords ought to be fixed above them in order to 

 ihorten the bearings, and fo far make the bodies firmer. 

 In a longer feries of piers this fhortening of the heads 

 can only be c> ntinued to the limit of depth necefTary to 

 fupport the flrains. 



The pier D prefTes the cords cc hy Its own we'ght, and 

 the load L. This prefllire caufes an equal pulling and 

 confequential reliOance in the tops of the piers B B. I he 

 pulleys of the piers C C" mull bear this double prefTure 

 = 2 L -f 2D. Thefe therefore prefs the cords ^ (6 with 

 faid weight and their own z=2L-|-2D-fCC. This dou- 

 bled = 4L-j-4D + 2CCisthc prelTure on the pulleys 

 of B B: But their heads are pulled up by L -}- D : The 

 difference of thefe forces added to their own weight is the 

 3 Y prelfure 



