the mean Denfity of the Earth. 705 
to a place to which they had before meafured with the 
tape line, and by it found to be 2844*8 feet; while 
the meafure of the fame by the rods is found to be 
2839*5 feet. The difference is 5I feet, a fmall part of 
which might be owing to the unftable Hate of the wooden 
Hands ufed in the lirft quarter of the bale; but the 
greater part of this difference is more likely to be owing 
to the uncertain way of meafuring with a tape, which, 
to fay nothing of the ground not being quite level, is 
liable to be ftretched more or lefs in length with dif- 
ferent degrees of tenfion, and to be variouffy warped in 
length by moifture. 
Of the meafurement of the bafe a (3 y in Rannoch, to the 
North-’WeJi of the hill of Schehallien. 
1 . One part of this bafe was meafured twice over in 
different ways. The part «/3 was carefully meafured on 
the 8th of October 1774 with a chain, and found to be 
63 chains and 40^ links, or 63*405 chains in length. 
Now on the 24th of the fame month the chain was 
meafured by means of the live-feet brafs ftandard, when 
the thet'mometer was at 38°!-, and the length found to be 
65*94542 feet. Hence then 65*94542x63*405 = 
4181*269 is the length of all the chains, to which, add- 
Vol. LXVIII. 4S ing 
