742 SEC. 15. GEOGRAPHY. 



Besides the addition of the movable level to the telescope, this instrument 

 possesses a new arrangement for its vertical movement. A small female 

 screw with right and left threads on opposite sides is inserted near the base 

 of the bearer. Corresponding to these threads are male screws tightly fastened 

 to the bearer, and, by turning the female screw to the inner or outer side, 

 the height of the telescope is increased or diminished. 



3050. Universal Theodolite (Bende's construction), hori- 

 zontal circle 12 m. diameter, divided to 20' and reading by two 

 verniers to 30". The divided limb is completely covered, and the 

 verniers are protected by "glass plates. Telescope, 15 lines aper- 

 ture, magnifying 35 times, adapted for reversal in the bearings, 

 lev el for setting; tangent screw exactly 1 mm. range. The vertical 

 arc 'is replaced by a long tangent screw with micrometer head, by 

 which vertical angles up to 45 can be measured. 



A. and R. Hakn, Cassel. 



By means of this instrument elevations can be measured directly with 

 the tangent instead of by the arc or its chord as hitherto. Its advantage over 

 other instruments consists in its peculiar construction, which admits of 

 using the micrometer screw in the measurement of angles up to 45, whilst 

 hitherto angles up to about 10 only have been so measured. The relation 

 between the reading on the screw and the height or distance to be measured 

 is a simple geometrical one. 



3051. Repeating Theodolite (No. 148), with stand and 

 leather case. Otto Fennel, Cassel. 



Covered horizontal circle, 14 cm. in diameter, graduated on silver to 20'., 

 and reading by vernier to 20 seconds. Achromatic erecting telescope. 

 Vertical circle with vernier reading to minutes. 



3052. Metford's Improved Theodolite, made by F. Pasto- 

 relli, under the direction of the inventor. Francis Pastorelli. 



DESCRIPTION OF THE INSTRUMENT. 



Levelling- Gear. It consists of three left-handed screws with the balls 

 fitting closely to their beds on the under surface of the traversing box ; they 

 afe secured by an elastic three-cornered plate, having boxes at their ends to 

 protect them from dust and grit. The lower ends of the three screws pass 

 through a triangular plate with broad ends, with sufficient spring to permit 

 the female screws to be slightly twisted. 



Traversing Stage. The main hollow centre of the instrument carries a 

 circular disc 3^ inches in diameter and T % of an inch thick ; the traversing 

 stage is a flat plate 5^ inches in diameter ; in its bottom the levelling screws 

 are seated as previously explained. The upper surface has a ring round 

 its edge the depth of the circular disc. There is a 2-inch hole in the 

 stage to let the plumb cord traverse with the instrument; the disc will 

 traverse 1 inch in any direction from the centre. To secure the instrument 

 there is an upper plate screwed to the ring, so that the stage becomes a very 

 shallow box ; there is also a washer that keeps out dust and grit. A three- 

 arm pinching screw running on the hollow centre secures the disc. 



Horizontal Limb and Vernier Plate. The horizontal limb and vernier plate 

 afe solid ; the latter has mounted upon it a compass, circular bubble, and a 



