III. MISCELLANEOUS. 627 



such, that besides lightness, sufficient stability is afforded for work of such *> 

 nature. The circles are divided to 10', so that they can be read without the 

 aid of the vernier to 5', and that the operator is not obliged to leave his 

 place during the work for the purpose of reading at the circles. 



For distance and height measurement, after the centre horizontal thread 

 has been adjusted to any point of the levelling staff, and the readings taken, 

 and the difference of the readings for the two threads, as well as the reading 

 of the centre thread, is noted in the field book. 



For the observation of the line of direction of other stations, the circles are 

 fixed by the clamping screws, and the exact adjustment obtained by meant? 

 of the micrometer screws. 



3080. Repeating Theodolite, with microscopes. 



S. C. Denncrt and C. W. Pap%, Altona. 



Repeating Theodolite with Reading Microscopes. The tripod stands on screws 

 which turn upon separate supports. The instrument is fixed to the stand by 

 a brass plate pressed up against the lower surface of the head by a screw and 

 spiral spring. The box rests upon an annular horizontal surface and can 

 be turned accurately round its axis, an arrangment which enables the repetition 

 movement to be quite accurately made. The vertical axis of hardened steel 

 and the horizontal circle are firmly united with the box, and round the 

 vertical axis turns a second box, having two double arms and serving as 

 a support for the bearers of the axis of rotation of the telescope, Avhich is 

 arranged for reversal and carries the vertical circle, with an arrangement for 

 vertical repetition movement. On the other end of the axis is the counter- 

 poise with a graduated circle, The telescope has an achromatic object glass 

 and orthoscopic eye-piece upon which a prism and sun glass can be placed. 

 The cross wires consist of spiders' threads and are held by adjusting screws. 

 Provision is made for illuminating the cross threads for observations at night. 

 The two levels are divided into sixths of degrees, and by means of two 

 screw microscopes accurate readings to 10 seconds may be obtained. 



3081. Theodolite for Horizontal Angles with microscopical 

 reading. Imperial German^ Navy {August Lingke and Co.)+ 



3082. Theodolite, with microscopical reading. 



Ed. Sprenger, Berlin. 



Theodolite, with horizontal and vertical circles 0'17 meter in diameter. 

 Both circles with microscopic reading to 2 seconds. Focal distances of tele- 

 scope, 0-32 ; magnifying power, 36 times. The tripod has a complete circle, 

 and a third microscope to screw for the exact and easy examination and 

 determination of the errors of division. The substructure and axis bearer 

 are of a single piece of cast steel, coated with chloride of platinum for pro- 

 tection from rust. The circles are solid and funnel-shaped, by which means 

 unequal expansion is avoided ; this is not the case with spoked circles. The 

 object-glasses are by Frauiihofer's successors in Munich. 



The Topographical Department of the "Royal Land Survey has exhibited 

 a telescope ruler, which is now introduced by the Department. It has double 

 verniers and a folding telescope, and is also furnished with a double bubble- 

 tube, rendering the instrument very useful for levelling. The distance-measure 

 is removable, but so contrived that no screw is visible outside, so that nothing 

 can act upon it. 



, 3O82a. 3-inch Theodolite. Three sheets of drawings. 

 " Dividing Machine." Troughton and Simms* 



Rr 2 



