622 SEC. 15. GEOGRAPHY. 



to an inverted 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. 



3O52a. 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. H. Husbands, Bristol. 



3052b. 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, Bristol. 



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 Constructing Scientific Instru- 

 ments. 



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 divisions ; the one to show degrees and 

 minutes, the other tangents. This latter division shows the fractional figure 

 of inclination at once without computation. 



3054. Gambey's Theodolite. 



3055. " Bussolen-Theodolite," a representation of an in- 

 strument invented by the exhibitor, for observing, with a micro- 

 scope, the exact position of the magnetic needle. 



Professor Joseph Schlesinger, Vienna. 



3056. Theodolite, horizontal circle, graduated scale of 13 cm. 

 diameter, divided on silver to J ; two verniers, reading 30 seconds, 

 two turning and regulating double magnifiers, with diaphragms, 

 On the alhidada a spirit level. Telescope of 28 mm. aperture, 

 32 cm. focal distance. Rarnsden eye -lens with movement. The 

 tripod can be shifted on the wooden stand. 



Frerk and Son, Hanover. 



The construction of the instrument is as low and simple as possible. The 

 rotating axis is directed from below upwards, and is situated between the 

 telescope supporters. It is made of steel, and the socket of the upper part 

 rests, by means of a regulating screw, on the hard glass point of the axis. 

 The low supports are fitted with easily opening cap-pieces, which act with 

 constantly uniform elastic pressure on the pivot of the telescope. By these 

 means the telescope can be easily adjusted, the pivots of the axis reversed, 



