III. SURVEYING. 745 



3076. Pocket Theodolite. 



F. W. Breithaupt and Son, Cassel. 



Capable of employment, on account of its small dimensions, in very con- 

 fined spaces, mines, &c. 



3077. Francis' Patent Pocket Theodolite, made by 

 Negretti and Zambia. George Francis, C.E. 



The improvements claimed for this invention are, 1st, its portability and 

 cheapness ; 2nd, its simpleness and easy application ; 3rd, the proportional 

 increase of length between the sights for dialling ; 4th, it is less liable to error 

 in taking horizontal angles ; 5th, its adaptability for taking the angle of an 

 underlie or gradient ; 6th, it requires little or no adjusting ; it combines with 

 the theodolite a clinometer, protractor, and plotting scales for reference, from 

 1 to 60 feet to the inch. 



At each setting of the instrument, the following observations can be taken : 

 1st, the horizontal angle of the back and forward sights to ^th part of a 

 degree ; 2nd, the magnetic bearing to ; and 3rdly, the rise or fall in the 

 sight to 1' and also in inches to the fathom for perpendicular and base. 



3080. Repeating Theodolite, with readiug microscopes. 



Dennert and C. W. Pape, Altona. 



The tripod stands on screws which turn upon separate supports. The in- 

 strument 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 body rests upon an 

 annular horizontal surface and can be turned accurately round its axis, an 

 arrangment which enables the repetition movement to be accurately made. 

 The vertical axis of hardened steel and the horizontal circle are firmly united 

 with the body and round the vertical axis turns the upper part, having two 

 double arms and serving as a support for the bearers of the axis of rotation 

 of the telescope, which is arranged for reversal and carries the vertical circle, 

 with an arrangement for vertical repetition. On the other end of the axis is 

 the counterpoise with a graduated circle. The telescope has an achromatic 

 object glass and orthoscopic eyepiece upon which a prism and sun glass can 

 be placed. The cross wires consist of spiders' threads and are held by ad- 

 justing screws. Provision is made for illuminating the cross threads for 

 observations at night. The two circles are divided into sixths of degrees, 

 and by means of two micrometers accurate readings to 10 seconds may be 

 obtained. 



3081. Theodolite for Horizontal Angles with reading 

 microscopes. Imperial German Navy (August Lingke and Co.). 



3082. Theodolite, with reading microscopes. 



Ed. Sprengcr, Berlin. 



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

 Both circles reading by microscopes to 2 seconds. Focal length of telescope, 

 0'32m. ; magnifying power, 36 times. The tripod has a complete circle, 

 and a third microscope for the exact and easy examination and determi- 

 nation 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 coned, by which means unequal 

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

 glasses are by Fraunhofer's successors at Munich. 



