III. SURVEYING. 743 



memorandum plate; also attached to it is the tangent motion. The limb i 

 divided to read 20 minutes, the vernier to 30 seconds. 



Bracket Support of Vertical Limb and Telescope. On the side of the main 

 pivot is attached a strong curved bracket with two arms at the top. This 

 bracket has a T section throughout ; to it is fixed the vertical circle and 

 female centre. The telescope and vernier circle, with its tangent motions, 

 are fixed on the male centre. The main spirit bubble is fixed at the back of 

 the vertical circle ; there is a screw in the bracket for perfecting its adjust- 

 ment. The axis of the telescope is suspended over the axis of the instrument, 

 and admits of a transit motion ; this is an important improvement. 

 '- Tripod Staff Head. This is an adoption of W. Froude, Esq., C.E., E.K.S., 

 by which steadiness is obtained, which is of great importance in taking angular 

 measurements. The cheeks are set wider apart, the leg joints being similar 

 to an inserted mortar with strong trunnions, which can be tightened in their 

 bisected cylindrical bearings by means of capstan-headed screws. As wear 

 goes on they can always be kept perfect;' this cannot be done with the 

 ordinary staff head. 



3052 a. Metford's 7-inch Theodolite, with curved arm 

 instead of the usual structure for carrying the vertical circle, and 

 telescope, mounted on his traversing stage, with legs, invented by 

 Mr. Froude. //. Husbands. 



3O52b. Metford's 4-inch Theodolite. Instead of being 

 mounted on the traverser is placed on the ball movement, and is 

 more especially recommended for very steep and hilly ground, and 

 for preliminary surveys. H. Husbands. 



3O52c. Theodolite. An extremely old, if not unique, instru- 

 ment, purchased by the late Sir James South as a rarity. In the 

 original oak box. G. J. Symons 



3053. Small Theodolite, for rapid operations. 



Geneva Association for the Construction of Scientific 

 Instruments. 



This instrument presents the following advantages : 



The telescope is reversible to give the correction of the zero of the 

 vertical circle. 



The position of the level is symmetrical. 



The divisions are strongly marked for rapid observations. 



The vertical circle has two graduations ; one to show degrees and 

 minutes, the other tangents. This latter division shows the reduction for 

 inclination without computation. 



3054. Gambey's Theodolite. 



Conservatoire des Arts et Metiers. 



3059. Large repeating Theodolite, with arc and altitude 

 circle, divided to 10'; with verniers for direct reading to 10'. 



Dennert and P ape, Altona. 



3060. Theodolite with circles of six and four inches. 



Julius Wanschaff, Berlin. 



This theodolite has been constructed (of greater durability than usual) for 

 naking very accurate measurements. The division is not the exhibitor's; 



