74 



BENJ. PIKE'S, JR., DESCRIPTIVE CATALOGUE. 



able observatory ; and it is doubtless one of the most gene- 

 rally useful instruments that has ever been contrived, being 

 capable of furnishing data to a considerable degree of ac- 

 curacy for the solution of a numerous class of the most use- 

 ful astronomical problems ; affording the means of deter- 

 mining the time, the latitude and longitude of a place, &c., 

 for which and many other purposes, it is invaluable to the 

 land-surveyor as well as the navigator. 



Price, $100 to $120. 



Single Framed, 50 to 80. 



" Ebony " 35. 



Fig. 97. 



Pocket Sextant. (Fig. 97.) This useful little instrument 

 is represented in the above figure. The principle of its 

 construction and adjustment is precisely the same as the 

 sextant before described ; a minute description, therefore, 

 would be little more than a recapitulation of what has 

 already been advanced. A is the index, which, instead of 

 being moved along the divided limb, ef, by the hand, has a 

 motion given to it by a rack and pinion, concealed within 

 the box, and turned by the milled head, B, which acts as the 

 tangent-screw does to the index of the large sextant. The 

 glasses (shown at C and D) are within the box, by which 

 they are protected from injury, and their adjustments, when 



