of the Plumb-line in India. 25 
(2) When the attraction of DRB is required : 
DE=25. 
p=2°96—2°68=0°28. 
h= ER=28°71. 
BR 28-71 
tana=tan ECR= perme 
a—AD+ AB= 124+ DE cot'e =222'145. 
p is the distance from B of the station. 
(3) When the attraction of ACB is required : 
i pose ol 
= 194 
a=25 cota=98'145. 
e— 5 tl. 
p is the distance from B of the station. 
I1.— Attraction of the Plain. 
Referring to figure 2, 
Let a be the width of the plain DR=230 miles. 
k the thickness of the crust=25 miles. 
p the distance from the southern edge of the plain 
of a station P where the deflexion is required. 
p the difference of ithe densities of the crust and the 
substratum =(°28. 
m the tangent of the angle at which the under side 
of the crust is depressed into the substratum 
= 3/230. 
1 the length of the area supposed rectangular, and 
conterminous with the mountain range. 
Then the attraction of the plain at P may be found from 
the following formula, it being premised that the attraction 
so obtained will be a negative attraction, due to the dis- 
placement of the dense substratum by the lighter crust thrust 
down into it. Consequently negative results will indicate 
deflexions towards R the southern edge of the plain, and 
positive ones deflexions towards C the “foot of the slope of 
the Himalayas. 
Attraction of | _ 
the plain j x 



f Se Er i ee a(mp Fit ot 
=p g (a—p)2+k(k+ma) 1+m? al ae 0? + kh?) + (mk—p)a 
be ak mp +k aes af a{ (a(L+ m”) + 2(mk—p)) 
Pig k?—p(a—p) _ 1+m? 2 govt pe+k 

se (a—p *+2 © “ma? 4) 
g°8e pt +k? oF ( OF); 
+1) 
