366 
Method of obviating 
and bowsprit, the blocks were put quite forward, that be* 
ing the part which presses them with the greatest force* 
As soon as the water was out of the dock, it was observ- 
ed that the horizontal wedges of nine and seven degrees 
had receded some feet from their original situations* 
This afforded Mr. Seppings a satisfactory proof, which 
experience has since demonstrated (though many persons 
before would not admit of, and others could not under- 
stand, the principle), that the facility of removing the 
blocks or wedges, was proportionate to the quantity of 
pressure upon them. The block of five degrees kept its 
place, but was immediately cleared, by applying the pow- 
er of the battering-rams to the sides of the outer ends of 
the horizontal wedges. The above experiments being 
communicated to the Navy Board, Mr. Seppings was di- 
rected to attend them, and explain the principle of his 
invention ; which explanation, further corroborated by 
the testimonials of his then superior officers, was so sa- 
tisfactory, that a dock was ordered to be fitted at Ply- 
mouth under his immediate directions. The horizontal 
wedges in this, and in the other docks, that were after- 
wards fitted by him, are of cast iron, with an angle of 
about five degrees and a half, which, from repeated tri- 
als, are found equal to any pressure, having in no in- 
stance receded, and, when required, were easily remov- 
ed. The vertical wedge is of wood, lined with a plate 
of wrought iron, half an inch thick. On the bottom of 
the dock, in the wake of each block, is a plate of iron 
of three quarters of an inch thick, so that iron at all 
times acts in contact with iron. 
The placing the sustaining shores, the form and sizes 
of the wedges, and battering rams, &c. ; also the process 
of taking away, and again replacing, the wedges of which 
the block is composed, are also exemplified by a model. 
The dock being prepared at Plymouth, in August, 
