42G The Account of a 
In the table containing the particulars of the operation it 
will be found, that the chain B was laid aside after measuring 
38 chains, on account of one of the links appearing to be a 
little bent. Before it was sent to Mr. Ramsden it was com- 
pared with the chain A (at first intended to be kept as the 
standard chain), when it was found to be only 4^ divisions 
longer ; which being i\ divisions less than the mean 6^ as 
found above, shows, that the chain B had lengthened divi- 
sions in measuring 38 chains ; for when Mr. Ramsden after- 
wards straightened the link, he could not perceive any dif- 
ference in its length. 
The remainder of the base was measured with the chain A 
(the chain B being kept as a standard), and when that was 
completed, a comparison was again made between A and B, 
when it appeared that A exceeded B by 14-^ divisions of the 
micrometer head; therefore the w r ear of A, by lengthening of 
the joints, in measuring 236 chains, was 14,2 — 4,5 divisions 
= 3,7 divisions of the micrometer. 
For finding the Rate of Expansion. 
The chain being placed in a right line, along the horizontal 
bottoms of the coffers, arid kept in a state of tension by a 
weight of fifty-six pounds, five thermometers were placed close 
by the chain ; one in the middle of each coffer; and the whole 
was covered with a white linen cloth, when the sun shone 
out. After remaining a few minutes, till the thermometers 
were nearly of the same temperature, a perfect coincidence 
was made on the register heads, at each end of the chain, and 
the thermometers noted. Every thing remained in this state 
till the coincidence at the weight end of the chain was ob- 
