Trigonometrical Survey. 6*31 



Tor and Cawsand Beacon. To reduce this angle to that formed 

 by the chords, 6" must be subtracted ; therefore, 125° 54' 24", 5 

 is the angle for computation. The sides Dumpdon and Rippin 

 Tor, Dumpdon and Black Down, (169014 and 153095,2 feet,) 

 with this angle, give the following triangle : 



Rippin Tor - - 25 36' 4^,5 



Dumpdon - 125 54 24,5 



Black Down - 28 29 31, which gives the 

 distance from Rippin Tor to Black Down = 286973,3 ^ eet - 



On referring to the observations made in 1797, on Black 

 Down, it will be seen that the angle between Rippin Tor and 

 the staff erected near Abbotsbury, was 3 8' 52",5, and the 

 angle between Pilsden and the same staff 45 16' 13" ; their 

 difference, 42 7' 2o",5, is the angle between Rippin Tor and 

 Pilsden. Now, if the angles of the triangles, five in number, used 

 in finding the distance between Rippin Tor and Black Down 

 have been observed correctly, and the calculations properly 

 made, the computed angle at Blackdown, between those sta- 

 tions, should be, of course, the same ; but the angle formed by 

 the chords of the arcs between Blackdown and Pilsden and 

 Dumpdon, has been found = 13° 37' 5Q",5, (which is very 

 nearly the same as the horizontal one,) and the angle between 

 Dumpdon and Rippin Tor = 28 29' 31", which it is also un- 

 necessary to correct : their sum is 42 7' 2i",5, the very angle 

 observed. It is not, perhaps, proper to dismiss this considera- 

 tion, without observing that this agreement affords a strong 

 proof of the excellence of our instrument, as the triangles, from 

 their magnitude and nature, are not so disposed as to favour the 

 comparison. 



4 M 2 



