47 



After these preliminary explanations, a detailed account is given 

 of the mathematical investigation, and the paper, which was illus- 

 trated with plans and geological sections, and a model of Arthur's 

 Seat, concludes with the following statement of the principal re- 

 sults : 



1 . " 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. 



2. "The calculated attractions of the mass of Arthur's Seat at 

 the three stations are, 



South Station. Arthur's Seat. North Station. 



2"-25 North. 0"-34 South. 1"'98 South. 



and, since the observed deflection at Arthur's Seat is 5"' 27, the 

 apparent effect of the Pentlands is 4"' 93 at the summit of the hill. 



3. " Of this deflection of 4"*93, the computed attraction due to the 

 configuration of the ground within a radius of fifteen miles accounts 

 for about 2"' 6 ; 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. 



4. "The deflection at the Royal Observatory, Calton Hill, being 

 5"- 63 South, exceeds that at Arthur's Seat by 0"70. Of this de- 

 flection, 0"'60 is due to the configuration of the ground comprised 

 within a circle of a mile and a quarter round the Observatory. 



5. "The latitude of Arthur's Seat or points in the neighbourhood 

 varies to the amount of 0"'02 between high and low water. 



6. "The mean density of the earth, determined from the observa- 

 tions at the three stations on Arthur's Seat, is 5'14, with a probable 

 error of +'07 due to the probable errors of the astronomical ampli- 

 tudes." 



