:6 c; 6 Col. roy’s Experiments for 
two barometers, gives the altitude intercepted between 
them, in toifes and thoufandth parts, reckoning the three 
figures to the right hand decimals, and the others inte- 
gers, the index being neglected. This temperature of 
69°. 32, when the logarithmic differences give the real 
height without any equation, is reduced to 39°.74, the 
new zero of Mr. de luc’s fcale, when his formula is 
adapted to Englifh fathoms and thoufandth parts, inftead 
of French toifes. And laftly, when the mean temperature 
jaf the air is above or below 39°.74,an equation, amount- 
ing to t < 5 6 ~oo parts of the logarithmic height for each de- 
gree of difference, is, in the firft cafe to be added to, and 
in the laft fubtra&ed from, that refult, in order to obtain 
the real altitude. 
In Mr. de luc’s book, the experiments for afcertain- 
•ing the expanfion of the quickfilver, are not given in 
detail; neither are the particular temperatures of the 
barometers fpecified. The winter feafon was however 
chofenforthepurpofe; one being left in a cold room, and 
the ether in a clofet, heated as high as could conveniently 
be fuffered. The operation having been repeated feveral 
'times without any effential difference in the refults, this 
•general conclufion is drawn, that between the tempera- 
lures of melting ice and boiling water, the expanfion of 
the 
