[ 3*3 3 
order to reduce the meafures to the temperature of 62° of Fahrenheit’s ther- 
mometer, which is the term to which the former operations of this kind 
have been reduced. For this purpofe, the rate of expanfion of brafs is taken 
from Mr. Smeaton’s experiment, made with a pyrometer of his invention 
(fee Philof. Tranf. Vol.XLVIII. Fart II.) which is of an inch 
upon a length of one foot for a variation of 180 0 of Fahrenheit’s thermome- 
ter ; whence the expanfion anfwering to four times the length of the brafs 
ftandard, or 20 feet, or the length of one level, would be th of an inch 
for the fame difference of the thermometer; and __!y S o 8 _^.th G f an inch for 
if of the fams thermometer. Therefore,, in order to find the correction of 
column 7th, the conftant quantity ,00258 was multiplied by the difference 
of 62, and the degree of the height of, the thermometer ; and that uroduCt, 
again multiplied by the number of levels meafured, gave the correction re- 
quired in inches and decimal parts of an inch ; which was additive or fub- 
traCtive, according as the thermometer was higher or lower than 62 degrees. 
In the following Procefs, the 
1. and 2 Columns contain the time of the day, M fignifying morning, A 
afternoon. 
3 _ - - _ the height of the thermometer at D°. 
4 - - - - the quantity, -in hundreth parts of an inch, that the two 
levels, taken together, were more or lefs than eight 
times the brafs ftandard, or 40 feet. 
4 - - — - the number of levels meafured between the times, that 
the levels’ themfelves were meafured with the brafs 
ftandard. 
6 - - - - the corrections, or quantity in inches, to be added to. 
or fubtra&ed from, the number of levels meafured 
each day, arifing from the- levels being more or lefs 
than the brafs ftandard. 
y - - - the correction, or quantity arifing from the thermometsr 
in inches. . 
Began, at the point N, to re-meafure the lines with two reCtangular levels, 
* 20 feet each in length. 
1768 1234 5 6 7 
February h 
$ 23 10 M 52, +,12 203 +12,18 — 4,97 
3. A 53 + »»* 
The breadthof Bran - 1 Q 0 
diwine the ift time J Ojlo + 0,49. 
D° a 2d, where we crofted 12,20 + 0,73 
Vo*, LVIII. S f 
