74© Col. roy’s Experiments for 
From the mean of tliefe obfervations, though the re- 
fults are irregular among themfelves, it appears fufli- 
ciently evident, that if the morning obfervations on Sa- 
leve had been retained, inftead of being made exceptions 
from the rule, the zero of the fcale would have de- 
pended about 8°; viz. from 69°. 3 to 6i°-4 of Fahren- 
heit, fuppoling always the equation 2.1 for each degree 
of temperature, and the French toife, as the ftandard 
meafure, to have been adhered to : for the French toife 
hears to the Englilh fathom, the proportion of 106575 
to 100000 ; wherefore -Ail i_=ii^2= 29°.4+32°= 69°.4, 
^denotes the relative pofitions of the two zeros, the inter- 
mediate equation (> C— being to be fubtradled, when the 
toife is made ufe of. But it hath been fhewn, that the 
mean expanlion of air is really greater, for fuch tempe- 
ratures at lead; as the barometer can be applied in, than 
what Mr. de luc fuppofed it, in the proportion of 245 to 
210; whence it follows, that ^=2 5°.i 8 + 32°= 57°. 18, 
will denote the relative politions of the two zeros ; which, 
inftead of almolt 30°, are only diftant from each other a 
little more than 25°. 
From what hath been Paid it is eafy to fee, that in cal- 
culating heights according to Mr. de luc’s rule, when 
the temperature of the air is below his zero, which we 
may 
