44 
Captain Kater/s account of the 
Before the plug was ground in its place a small hole was 
drilled through the side of the scale into the conical 
aperture. 
The microscopical apparatus employed on the present 
occasion has been described in the paper upon the comparison 
of various British standards of linear measure before quoted. 
The cross wires of the microscopes being brought respec- 
tively over zero, and 36 inches upon Sir G. Shuckburgh's 
scale, the apparatus was transferred to the new standard, and 
the intersection of the cross wires of one of the microscopes 
placed upon the centre of the fixed dot. The moveable dot 
was then brought by turning the brass plug to the intersec- 
tion of the cross wires of the other microscope. 
The distance of the dots was repeatedly compared with 
Sir G. Shuckburgh's standard upon different days, in order 
to ascertain that no perceptible error remained. A drill was 
passed through the hole in the side of the scale, and the 
brass plug carefully pierced through ; a pin was then driven 
into the plug so as to render any change of position impossi- 
ble, and the projecting part of the plug was cut off. 
The standards being thus finished, they were again com- 
pared with Sir G. Shuckburgh’s scale, and it was with 
surprise and disappointment that I found the whole of them 
apparently too short. They had been adjusted upon a board 
of mahogany carefully planed, and the table upon which they 
were now placed was so flat as to occasion little alteration in 
a spirit level passed along it. The error of the standards 
was however far too considerable to be attributed to any 
curvature which on this occasion could take place, and it was 
