The Account of a 
art. nr. Reduction of the Base measured on Salisbury Plain, 
to the Temperature of 62°. 
The overplus of the 366th chain was measured 
by Mr. Ramsden, and found to be 9,939 feet ; there- Feet, 
fore the apparent length of the base was - 36590,061 
By the measurement in the Duke of Marlborough's 
riding-house, the chain A was found to exceed 100 
feet in the temperature of 54 0 , by o, 1 1425 inches ; to 
which adding half the wear, namely, inch, we 
get 0,1 ^ 7 feet for the excess of the chain's length 
above 100 feet ; therefore °~~ x 3 65,9 (chains) = 
3,542 feet, is the correction for excess and wear; 
which add - -{" 3,542 
The sum of all the degrees shown by the thermo- 
meters, was 146051; wherefore - 1 406 51 — 54 0 x 365,9 
x " - ° 7; = 5,232 feet, is the correction for the mean 
heat in which the base was measured above 54 0 , the 
temperature to which the chains were reduced ; and 
this add - - - - + 5,232 
Hence these corrections, added to the apparent — — 
length, give - 3 6 59 8 > 8 35 
Again,. for the reduction to the temperature of 62°, 
viz. for 8° on the brass scale, we have ? . 01 . 237X 365,9x8 0 
12 
= 3,017 feet; which subtract - - — 3,017 
By the tables, the sum of the versed sines of the 
