79 
various British standards of linear measure * 
bent round the edges of the 40 inch bar, so that the upper 
surface of the bar was in perfect contact with the brass, 
the side pressure being just sufficient to prevent any change 
of position in the brass, unless when moved along the bar 
by hand. A fine line, about the eighth of an inch long, 
was now drawn on one of the gold pins at right angles to 
the bar, and a similar line was traced on the piece of brass, 
which was placed so as to cover the other gold pin. The 
intersection of the cross wires of the tracing microscope was 
carefully adjusted to this last line. 
Mr. Ramsden’s bar, upon his decease, became the property 
of Mr. Berge, whose successor, Mr. Worthington, kindly 
granted me access to it, and facilitated my examination by 
every assistance in his power. The bar was placed in his 
workshop on tressels, and its surface carefully brought into 
the same plane, which was ascertained by stretching a thread 
from end to end. 
The 40 inch bar was laid near Mr. Ramsden's bar on 
the 12th of April, 1820, and a thermometer placed upon it. 
Three thermometers were also arranged at equal distances 
along Mr. Ramsden’s bar. 
On the 13th of April I commenced my examination. The 
intersection of the wires of the one microscope being placed 
on the centre of the left hand dot, the intersection of the 
wires of the other microscope was brought, by means 
of its micrometer screw, to the centre of the right hand 
dot, and the reading of the micrometer registered. In this 
manner the six intervals of Mr. Ramsden’s bar were compar- 
ed in succession. It may be necessary to remark, that as 
the microscopes invert, the readings are to be taken in a 
