686 Sir g. shuckburgh’s Letter to Col. roy on 
Thus it feems, that the error of my tables, from a 
mean of all thefe obfervations, amounts to + 10 *° 00 ; of 
yours, to + : but it mu ft be remarked, that the ftan- 
dard temperature, from whence I compute, is 31 ",24 of 
Fahrenheit, whereas in your computations it is affumed 
at 32°,o ; this difference of o°,76 is equal to the 
correction for the expanfion of the air: if then we were 
to fet out from the fame zero, viz. 3 2 0 (which I have 
propofed, fee p. 5 69. of my memoir, Phil. Tranf. vol. 
LXVIl.) the error of my tables, according to your ob- 
fervations, would become only , that of yours re- 
maining -n-'-™. I would by no means from hence con- 
clude, that any preference is to be given to the former, 
but would fay, that in molt practical obfervations, in 
thefe countries at leaft, it is indifferent which method is 
ufed. Thefe fame companfons alfo afford us another 
piece of information, viz. that under fimilar conditions 
the denfity of the atmofphere is the fame, whether un- 
der the parallel of 46 or 56 degrees of latitude. Till, 
therefore, more accurate obfervations than thofe of Mr. 
bouguer !a> can be obtained in the neighbourhood of 
the 
( a ) Mr. boucuer’s obfervations I hold inadequate in fuch an inquiry, not 
only on account of their incorreftnefs (for they are related only to the J of a 
French line), but particularly inconclufive, allow them all the precifion you 
pleale, as they were not fynchronous; infomuch, that we are uncertain whether 
thofe obfervations, which fhould be correfponding in point of time, were made 
within fix months of each other : and with regard to the temperature of fome of 
them 
