42 
THE WELDON RANGE-EINDER. 
proportional to tlie sides of tlie triangle which, converge on the distant 
object. He reasoned thns :— 
Fig. l. 
A 
In an isosceles triangle ABC, of which the angles ABC, ACB are 
each 88° 34' 3", and AJD is a perpendicular, 
AB — BT) sec 88° 84' 3" 
= 20 BO. 
He applies this reasoning practically thus :—• 
Suppose an observer (Fig. 2) at C, with an instrument capable of 
reflecting an angle of 88° 34' 3", sees A reflected along a line CF. If 
an observer provided with a similar instrument moves in the direction 
Fig. 2. 
A 
