C «5S 3: 
XXXIV. Experiments and Obfervations made in Britain^ 
in order to obtain a Rule for meafuring Heights with 
the Barometer . By Colonel William Roy, F. R. S. 
: Read June 12 and 19, and Nov. 6 and 1 3, 1777. 
I N T R O D U C T I O N. 
T N philofophical inquiries of every kind, where any 
-*• point is to be afcertained by experiments, thefe can- 
not be repeated too often, nor varied too much, in order 
to obtain the truth: for even when the utmoft precau- 
tion hath been ufed, and the greateft pains have been 
taken, it rarely happens, that they agree fo exactly, as 
to leave no room for doubt. Were it poffible at all 
times, to have experiments made in circumftances per- 
fectly fimilar, a confiderable degree of confiftency 
might naturally be expected among the refults, where- 
of the mean would determine the point in queftion; 
but different men, making ufe of different inftru- 
ments, have different modes of conducting their ope- 
rations, each purfuing the traCt that feems to him the 
moft likely to infure fuccefs. Hence it is that a variety 
of 
