KB<:i^P5JTV OF llVTMiO SHIPS. 1^3 . 



praAIce of lifting Uierij, and which are removed by the 



prefent plan j that which relates to maiuial labour deferve^ 



particitiar attention; twenty men being lutEcient to fulpend Twenty men 



a iirft rate, whereas it would require upwards of 500 to lift qJ-^J^q^ «P^^ _a^ 



her. The fituation which Mr, Seppingft held in Plymouth- " '' 



yard, attached to |iini, in a great degree, the fl)oring and 



lifting of ftiips, as well as the otlier practical part of the pfo- 



feffioTi of a tbipwright, Here he had an opportunity ofHjftcryy 



obferving, and indeed it was a fubjecl of general regret, how 



pMic\i time, expenfe, and labour, were required in lifting a 



fliip, particularly Oiips of the line. This induced him to con- 



fid^r whether fome contrivance could not be ^adopted to 



obviate thefe evils. And it occurred to him, that if he could 



fo confliu6l the blocks on which the (l)ip refts, that the weight 



of the ftiip might be applied to affifl in the operation, ho Ihould 



accomplifli this very defireable end. In September 1800, 



the (lioring and lifting the San Jofef, a large Spanifn firfl-rate^ 



then in dock at Plymouth, was committed to his direfSlions ; 



to perform which, the afl] (lance of the principal part of the / 



artificers of the y^rd was requiiite. |n eondu6ling this butinefs, 



the plan, which will be hereafter defcribed, occured to his 



m'md ; and from that lin^e, he, by various experiments, 



proved his theory to be corred : the blocks, conilru6led by The contrivance 



him, upon which the ftnp refts, bging fo contrived, that the jf^^^^j^f^^j^'^' 



facility in removing them, is proportionate to the quantity of hoHzontaf 



preflure; and this circumt^anpe is always abfolutely under "'^jSes, 4^mg 



. , ■^ •' under an obtufc 



Cfimmand, by increafing or dipiini^iing the ^ngle of three vertical v,redge, 

 wedges, which conftiti|te one of the blocks ; two of which 

 are horizontal, and one verticals By enlarging the angle which by the 

 pf tjie horizontal wedges, the vertical wedge becomes of ^^J^^ 5fTe?dful 

 confequence rnore acute ; and its power may be fo increafed, difplace the 

 that it tliall have a great tendency to difpiace the horizontal °^^^'*' 

 wedges, as w^s proved by a model, which accont^panied the 

 ftatement to the Society ; where the power of the fcrevy is 

 ukd as a fubilitute for the prelTure of the fliip. 



Mr. Seppings caufed three blocks to be made of hard wood Experiments, 

 agreeable to his invention, and the wedges of various angles. 

 The horizontal wedges of the fir(l block were nine degrees; 

 ot' the fecond, feven ; and of the third, five ; of courfe, the 

 angle of the vertical wedge of the firft block was 162 degrees; Angles of tU« 

 of the fecond 166; and of the third, 170 Jheie blocks, or^^'^S"' 



wedges. 



