58 



BENJ. PIKE S, JR., DESCRIPTIVE CATALOGUE. 



raise the prism in its socket, b, until you obtain distinct 

 vision of the divisions on the card, and standing at the 

 place where the angles are to be taken, hold the instrument 

 to the eye, and looking through the slit, c, turn round till 

 the thread in the sight- vane, bisects one of the objects 

 whose azimuth or angular distance from any other object 

 is required ; then, by touching the spring, e, bring the needle 

 to rest, and the division on the card which coincides with 

 the thread on the vane, will be the azimuth or bearing of 

 the object from the north or south points of the magnetic 

 meridian. Then turn to any other object, and repeat the 

 operation ; the difference between the bearing of this object 

 and that of the former, will be the angular distance of the 

 objects in question. Suppose the former bearing to be 40 

 30', and the latter 10 15', both east, or both west, from 

 the north or south, the angle will be 30 15.' The divi- 

 sions are generally numbered 5, 10, 15, etc., round the 

 circle to 360. A stand can be had with the instrument, 

 if required, on which to place it when observing, instead of 

 holding it in the hand. Price, $16.00 and $20.00. 



The Plane- Table. (Fig. 90, as below.) Before the theo- 

 dolite came into general use, the plane-table was extensively 

 employed in the practice of surveying ; it is still sometimes, 

 chough seldom, used in surveying small plots of ground, or 



Fig. 90. 



