Measurement of a Bafe on Hoimfiow Heath. ' 4 5 ~ 
It Will be remembered, that in carrying on the operation 
with the deal rods, double pickets were left in the ground at 
the twenty-feventh Nation, aniwering to the extremity of the 
Siotn rod from the fir if, or the 560th from the I aft end of 
the bafe. Now, on arrival at this point, the 560th glafs rod 
•overhiot the iilk thread,- ftretched from one picket to the other, 
2.525 inches. Here again we find, that the lengthening * of 
the deal rods from the moifture of the atmofphere differs but 
little from what it has been eftimated at by comparifon with 
the ftandard, being over-rated only two-tenths of an inch on 
tne 560 iods. In this day s operation, in palling the bridge laid 
over the old river, the meafurement, inftead of being made i U 
the hypothenufal, was carried on in the level line, for the 
fpace of twenty rods, namely, fifteen rods of the twenty* 
feventh, and five of the twenty-fixth hypothemife ; wiiich 
occafions the alteration in the reduction of theft: two f paces, 
marked with afterifks in the general table. 
As fome trouble bad been found to attend the crofting of 
the great road, in the firft meafurement, owing to the num- 
ber of carriages that were continually palling, the depth of 
* 560 deal 
rods rr 
1 1 200 ft. 
lii. 
+ 1.39° for i° excefs of heat of the brafs feale from 62® 
to 63°. 
-f 5.258 eftimated expanfion from moifture, 
+ 6.648 equation of the 560 deal rods. 
560 glafs 
rods — 
1 1200 ft. 
+ 8.343 for 6° excefs of heat of the brafs feale from 62° to 68 s 
+ 1.821 obferVed expanfion of glafs [from columns nth 
— l.iqi obferved contraction of ditto j and 12th 
-2.525 over-fliot the filk-thread. 
+ 6.448 equation of the 560 glafs rods. 
©.-200 ( •^ ) '®' erence over-rated in the expanfion of the e6o 
l deal rods. 
o © o 2 the 
