AND THE MEAN SPECIFIC GRAVITY OF THE EARTH. 
605 
The number of circles already drawn round Arthur’s Seat is 21. the last nine being 
drawn according to the law r„+i=fr„: if we draw seven more according to the same 
law, this will carry us slightly beyond the boundary of the county. The sums of the 
heights in the different rings will then be as follows : — 
22nd. 
23rd. 
24th. 
25th. 
26 th. 
27th. 
28th. 
11850 
12050 
12850 
15950 
17100 
18750 
16800 
the sum of which is 105350. The consequent deflection will be, using the same value 
of X, namely '5173, 
0"*00003027 X 105350 x '5 173 = l"-64. 
To this we have to add the quantity obtained for the preceding nine rings, namely, 
1"'69 j 7 or 0"‘88, making altogether 2"’52 due to the high ground to the south within 
the county of Edinburgh. 
From the height of the country in the north of Peebleshire, it seems probable 
that when the calculation can be carried into that county, a sensible addition to 
the quantity above determined will be obtained, and that the whole of the 5" may 
possibly be accounted for. 
In conclusion, the principal results arrived at are these : — 
1st. The effect of the attraction of the Pentland Hills is observed in nearly equal 
amount at each of the three stations on Arthur’s Seat. 
2nd. The calculated attractions of the mass of Arthur’s Seat at the three stations are. 
South Station. 
Arthur’s Seat. 
North Station. 
2"‘21 North. 
0"*37 South. 
2"*00 South. 
and, since the observed deflection at Arthur’s Seat is 5"'25, the apparent effect of the 
Pentlands is 4"'88 at the summit of the hill. 
3rd. Of this deflection of 4"’88, the computed attraction due to the configuration 
of the ground within a radius of fifteen miles accounts for about 2"'5 ; and, inasmuch 
as we know that the igneous rocks of Arthur’s Seat and the Pentland Hills have an 
origin at a great depth below the surface of the earth, the difference between the 
observed and computed attraction is probably owing in part to the high specific 
gravity of the mass of rock beneath them. 
4th. The deflection at the Royal Observatory, Calton Hill, being 5"’63 South, 
exceeds that at Arthur’s Seat by 0"'70. Of this deflection, 0"'60 is due to the con- 
figuration of the ground comprised within a circle of a mile and a quarter round the 
Observatory. 
5tb. The latitude of Arthur’s Seat or points in the neighbourhood varies to the 
amount of about 0"’02 between high and low water. 
6th. The mean density of the earth determined from the observations at the three 
