528 Sir george shu cic burgh’s Obfervations 
have reckoned the equation for the expanfion of quick- 
filver =,00323 inch for every degree of Fahrenheit’s 
thermometer in a column of 30 inches, inftead of ,003 1 2 
which Mr. de luc ufed; the former I had collected from 
fome of my own experiments made at Oxford in the 
beginning of the year 1773: this difference will not, 
however, occafion an alteration in the refult of any one 
of my obfervations of more than five inches, and may 
therefore be confidered as of no account. Of the real 
value of this correction I fhall fpeak more hereafter. 
The barometer was fet up on the mountain at one 
o’clock, and left an hour and a quarter to acquire the 
temperature of- the tent in which it was placed, before 
the firft- regular feries of obfervation was taken. The 
fucceeding obfervations were made at intervals of near 
an hour each. I have ventured to fet down the height 
of the barometer to ,0001 inch; but this is only the 
mean from three or four readings off. It feems that the 
heat of the tent was confiderably greater than that of the 
external air.; this, however, can only influence the ex- 
panfion of the quickfilver, Ihewn by the attached ther- 
mometer, and not the preffure of the atmofphere. 
Laftly, the. true difference in the height of the refervoirs 
of the two barometers, by comparifon with a and c, was 
-found equal 2831.3 feet geometrically. 
Com* 
