estimated in parts of the English standard. 109 
parts of its length for one degree of Fahrenheit, and as 
this is the expansion used by the French in adjusting the 
length of their metre, it must be employed on the present 
occasion. The metre being taken at 32 0 , the expansion for 
the difference between this and the temperature of measure- 
ment, must be subtracted from the apparent length of the 
metre. The English standard temperature is 62°, therefore 
if the temperature of measurement be under this, the expan- 
sion of the scale for such difference of temperature must be 
deducted from the length of the metre before obtained. 
These two corrections are combined in the column entitled 
“ correction for temperature/’ Sir G. Shuckburgh’s standard 
scale is of cast brass, and as I could not conveniently deter- 
mine its actual expansion with that degree of accuracy that 
would have satisfied me, I have taken for it, the mean result 
of two experiments made on plate brass, which gave me an 
expansion of ,0000101 parts of its length for one degree of 
Fahrenheit. The mean of most of the experiments made 
on the expansion of brass gives ,0000104, and had Iemployed 
this last number instead of my own, the difference in the 
length of the metre would have been utterly inconsiderable. 
Supposing then both metres to be of equal authority, we 
have for the length of the metre a traits 39,37076, and for 
that of the metre d bouts 39,37081 inches ; the mean of which, 
39 > 37 ° 79 > ma y be taken for the length of the metre in inches 
of Sir G. Shuckburgh’s standard scale when each is brought 
to its proper temperature.* 
* The length of the metre compared with Bird’s parliamentary standard is 
39,37062 inches. 
London, November 1817. 
