Mtafurement of a Bafe on Hounflow-Heath. 457 
Table of the Expanfion of the Deal Rods. 
N° of 
Hour of 
Temp. 
Obferv- 
Deci 
Equation 
Equation 
Total 
Days. 
rods 
comparifon. 
of the 
ed ex- 
mal 
for the 
for the 
expan - 
meaf. 
air. 
panlion. 
mean. 
meaf. rods. 
llaridard. 
fion. 
h. , 
In. 
In. 
In. 
In. 
July 16 
105 { 
4 oA.M. 
6 oP.M. 
48 1 
62 J 
Teth 1 
O / 
0.0 10 
1.050 
0.2625 
1.3125 
r 95 { 
7 oA.M. 
6 oP.M. 
62 | 
Tffth j 
0.0 10 
1.95° 
0.4875 
2-4375 
2 3 
240 { 
9 oA.M. 
6 oP.M. 
6. , 
54 J 
Tff 
-57 J 
0.021 
5.04° 
0.6000 
5.6400 1 
( 
7 30A.M. 
6l 
h J 
S i 
0.6650 
24 
270 J 
11 15A.M. 
66 
0.033 
8.910 
9 - 575 ° 
l 
5 45 P- M - 
64 
c 
Aug. 2 
270 i 
8 30A.M. 
7 oP.M. 
66 
& 7 § 
T o } 
0.0125 
3-375 
O.6650 
4.0400 
3 
29° j 
7 oA.M. 
5 oP.M. 
56 ) 
75 J 
*0 } 
0.017 
o -493 
0.7250 
1.2180 
Total 
137° 
- 
- - 
— — 
- - 
20.818 
3-405 
24.223 
N. B. Although the rods were not compared with the ftandard on the 1 6th 
of July, yet the expanfion probably was, 
and therefore has been eftimated, at 
the fame rate 
as it was found on the following day. 
I 
By examining the preceding table, it will appear, that the 
total expanfion on the 1370 deal rods, including the fmall 
equation for the lengthening of the ftandard, amounts to 
24.223 inches, or 2.02 feet; which being added to the appa- 
rent length of the bafe 27404.31 feet formerly obtained, we 
fhall have, for the hypothenufal length, 27406.33 feet: . and 
from this deducing 0.07 foot, the excefs of the hypothenulal 
above the bafe line, or the reduction contained in the feventh 
column of the general table of the bafe, there will remain 
27406.26 for the diiiance given, by the deal rods, between the 
1 centers 
