On oluiaii/ig the Necessity ofUfthig Ships. 243 



♦under command, by increasing or diminishing the angle of 

 three wedges, which constitute one of the blocks ; two of 

 which are horizontal, arKi one vertical. By enlarging the 

 anofle of the horizontal wedges, the vertical wedge becomes 

 of consequence more acute ; and its power may be so in- 

 crea'^ed, that it shall have a great tendency to displace the 

 horizontal wedges, as was proved by a model, which ac- 

 companied the statement to the society ; where the power 

 of the screw is used as a substitute for the pressure of the 

 ship. 



Mr. Seppings caused three blocks to be made of hard 

 wood agreeable to his invention, and the wedges f)f various 

 angles. The horizontal wedges of the first block were 

 nine degrees ; of the second, seven; and of the third, five ; 

 of course, the angle of the vertical wedge of the first block 

 was 162 degrees; of the second, ]66', and of the third, 170. 

 These blocks, or wedges, were well executed, and rubbed 

 over with soft soap for the purpose of experiment. They 

 were then placed in a dock, in his majesty's yard, at Ply- 

 mouth, in which a sloop of war was to be docked : on exa- 

 tiiining them after the vessel was in, and the water gone, 

 they were all found to have kept their situations, as placed 

 before the ship rested upon them. Shores in their wake 

 were then erected to sustain the ship, prior to the said 

 blocks being taken i'rom under the keel. The process of 

 clearing them was, by applying the power of battering- 

 rams to the sides of the outer ends of the horizontal wedges; 

 alternate blows being given fore and aft ; by which mean* 

 they immediately receded, and the vertical wedges were 

 disengaged. It was observed, even in this small ship, that 

 the block which was formed of horizontal wedges of nine 

 degrees, came away much easier than those of seven, and 

 the one of seven than that of five. In removing the afore- 

 said blocks by the power of the battering-rams, which were 

 suspended in the hands of the men employed, by their 

 holding ropes passed through holes for that purpose, it was 

 remarked by i\Ir. Seppings, that the operation was very la- 

 borious to the people ; they having to support the weight 

 of the battering-rams, as well as to set them in motion. 

 He then conceived an idea of affixmg wheels near the ex- 

 tremity of that part of the rains which strikes the wedges. 

 This was done before the blocks were again placed ; and it 

 has since been found fully to answer the purpose intended, 

 particularly in returning^ the horizontal wedges to their 

 original situations, when the work is performed for which 

 they were displaced : the wheelsalsogivlng a great increascof 

 Q 2 power 



