350 BEXJ. PIKE'S, JR., DESCRIPTIVE CATALOGUE. 



fixed. The telescope is fixed to a horizontal axis ; it has 

 a free vertical movement, and may be reversed by turn- 

 ing over. There is a clamp-screw near the axis for fix- 

 ing it, and a tangent-screw, Q, for slow motion. The 

 focus of the cross hairs is adjusted by sliding in or out the 

 eye-piece. The object-glass is brought to a proper focus 

 by turning the milled head, P. The central adjustment 

 of the cross hairs is made by four screws, N, at opposite 

 points in the body of the telescope, and the eye-piece 

 fixed central by the four screws, O. These instruments 

 when delivered are all accurately adjusted, but should 

 they at any time be deranged, directions for their adjust- 

 ment equally applicable to these instruments may be 

 found under the article Theodolite (Fig. 99), in this work, 

 page 85. 



When required, a vertical circle is fixed to the axis, as 

 in the preceding instrument, and also a level attached to 

 the tube of the telescope ; the former would cost about 

 ten dollars additional, and the latter five dollars. In 

 the construction of the transit instrument these are not 

 usually wanted. These instruments are finished bright, 

 or polished brass, and dark or bronzed, the latter being 

 preferred by some on account of its being more agreeable 

 to the eye in a bright sun. A brass plumb-bob accom- 

 panies the instrument which is packed in a mahogany 

 case. Price $150. 



Chamberlain's Patent Draughting Board (Fig. 786), 

 For engineers, surveyors, designers, builders, &c., &c. 



Description of Chamberlain's Patent Draughting-Board. 

 (Fig. 786). No. 1. Moulding, A, B, C, D ; scales, c,f, 

 g, h; draught sheet space, a, b, c,d; ketch-heads, i, i, i, i; 

 equator, E, F ; meridian, G, H ; design, J, J ; title, A ; 

 copyright, B ; device, D ; points of compass, C. No. 2. 

 Ketch-shanks, i, i, i, i, i, i, i ; ketch-bars, o, o, o, o ; legs, 

 /, Z, Z, I ; spring bale, n, n, n, n, n, n ; brackets, k, k ; 

 connections, m, m, m, m; panel, , b, c, d. No. 3. T 

 rule ; tongue, T, T ; right-angled back, U, U ; multan- 

 gular baclv V, V ; adjusting screw, S ; size of board, 

 23 by 29 inches. The moulding guards the surface and 

 guides the T rule. The scales of degrees and inches are 

 extensive and minutely divided. They are numbered 

 each way from the centres, E, F, G, H, and the subdivis- 



