438 The Account of a 
which were proposed for this purpose, that of heavy iron can- 
non was adopted, having been previously sanctioned with 
the approbation of Mr. Ramsden, and other competent judges. 
Two guns were therefore selected at Woolwich by order of 
the Master-general, from among those which had been con- 
demned as unfit for the public service, and sent to Hampton 
by water. 
The placing of these guns accurately being an operation of 
a delicate nature, and attended with some difficulty, on account 
of their great weight, the mode of performing it was very de- 
liberately considered ; and every precaution afterwards taken 
to render the operation unexceptionable. The method was as 
follows. 
Four oaken circular pickets, of 3 inches diameter, were 
driven into the ground, at the distance of 10 feet each from 
the centre of the pipe, two of them being in the direction of 
the base, and the others at right angles to it. Melted lead was 
then run into a hollow made in the head of each picket, and 
afterwards filed off perfectly smooth. On the brass cup, be- 
longing to the Royal Society, being adjusted in the pipe, silver 
wires were stretched from the heads of the opposite pickets, 
and moved till their intersection coincided with the centre of 
the cup ; and in this position a fine line was drawn on the 
lead of each picket, exactly under and in the direction of the 
wire. This operation being performed, and the truth of it re- 
examined, the pipes were taken out of the ground, in doing 
which it became necessary to make an excavation of about four 
feet, in order to clear the circumference of the wheel. It had 
been at first intended to have inserted the gun so far in the 
ground as that its muzzle should be even with the surface of 
