MEAN DENSITY OF THE EARTH.

Tract 26.

But since 62 — 40 = 22 , therefore the .reduction for the stateof the air is -22x T7 ^ M x 4185=—‘989, which being ap-plied to the above sum, there remains 4183-79 as correspond-ing to the state of 62° of the thermometer. From this lastnumber deduct its TT i TO th part, viz, -232, and there results4183-558 for the correct length of the part a/3, as determinedby this very accurate method ; which is but about a foot anda half more than what it was found to be by the less accuratemeasure by the chain, which is a nearer approach to an equa-lity than could well be expected.

To determine now the whole length of the base ay ; bytaking the whole sums there are found to be 146a with 144nand 779-78 inches of the odd parts.

Now 146a = 146 x 20T08|. = 2935-890144b = 144 X 20-112| = 2896'248779-78 inches = 64'9S2

The sum or «y, unreduced, is 5897-120

The correction for the thermometer is — 22 x ^^5 x5897 = — T394, which being applied to the number above,there results 5895-726 ; and this again being diminished byits -j-g-i^.g.th part, or -327, there remains 5895 - 399 feet, for thecorrect measure of the base ay in the vale of Rannoch.

There is no occasion here to explain the maimer of mea-suring these two bases by the twenty-foot rods, as that hasbeen very circumstantially done in vol. 65 of the Phil. Trans,for the year 1775.

The following sh irter lines were also measured, as theyhappened to be wanted in different parts of the survey.

nearly horizontal.

Ft.

In.

a'5'

=

269

4'

Nrt

=

93

6

KC

=

94

10

KE

240

10

ac

-

9

9

iin

=

7

10

cn

=

1

11