III. SURVEYING. 749 



and, like the spirit-level, may be reversed ; the bearer, furnished with a double 

 altitude arc, lies with its axis in closed rests, and has a vertical movement 

 and a fine adjustment by means of micrometer screws ; a spirit-level on the 

 head of the axis serves for its accurate adjustment in a perpendicular position. 

 Horizontal circle, with glass coverings to the verniers. Constructed in 1854 

 by F. W. Breithaupt and Son. 



4561. Photograph of the Universal Instrument of Luigi 



Belli, for levelling operations, trigonometrical and graphic, by 

 being adapted to the Prsetorius table. Luigi Pelli, Florence. 



The universal instrument of Luigi Pelli serves for levelling operations, 

 being mounted like the most exact telescope-levels. It serves for the same 

 trigonometrical operations as the theodolite, having an azimuth circle similar 

 to that of the repeating theodolite, but with only two verniers. The alidade is 

 placed so as to coincide with the plane of the tablet by means of a central screw 

 situated in the column which sustains the telescope. A point fastened with 

 springs within the screw marks on the paper the centre of the azimuthal 

 circle. In this manner angles may either be measured or plotted at once. 



313O. Photograph of an Altitude Circle, objective of 

 2*1" aperture, diameter of circle 10^". Latest construction of the 

 instruments of a similar kind extensively in use in Russia for 

 determining geographical positions. 



A. Repsold and Sons, Hamburg. 



b. REFLECTING CIRCLES. 



30G1. Ten-inch reflecting Prismatic Circle, similar to 

 that of Pistor-Martin. Julius Wanschqff\ Berlin. 



3087. Reflecting Prism Circle, 10 in. diameter. 



Meissner, Berlin (If. Muller and F. Reinecke). 



3088. Reflecting Prism Circle, 6 in. diameter. 



Meissner, Berlin (If. Muller and F. Reinecke). 



Th3 reflecting prism-circles can be recommended on account of their 

 excellent execution, in optical as we'll as in mechanical respects, and also on 

 account of their cheapness. 



3115. Reflecting Circle, according to Pistor and Martins. 



F. W. Breithaupt and Son, Cassel. 



3115a. Improved Reflecting Circle of Fister and Mar- 

 tins. The Pulkowa Observatory. 



A full description of the patent reflecting circle of Pister and Martins in its 

 original construction is given by the inventors in the Astronomische Nachrich- 

 ter, vol. xxiii. In the form exhibited general improvements are introduced by 

 the inventors on Professor Dallen's suggestion ; for instance, all correction 

 screws of the prism are removed, the stifihess of the main body is considerably 

 increased, the different parts of the instrument are more symmetrically dis- 

 posed, the telescope and the dark glasses are separated from the radius, on 



