III. SURVEYING. 753 



optical axis of the telescope and the line of collimation ; the main bubble is 

 dead fitted ; it neither admits nor requires adjustment, as it is done in con- 

 struction. 



Diaphragm. The diaphragm with its collimating screws cannot be dis- 

 turbed. A grooved channel is formed in the eye end of the telescope, into 

 which they are sunk, and a cylindrical ring conceals them from sight, thus keep- 

 ing them intact. This is one of the important adjustments of the instrument. 



3112a. 12-inch Level mounted on the Ball movement. 



//. Husbands. 



The 12-inch level is mounted on the ball arrangement, the combined inven- 

 tion of Mr. Metford and Mr. Froude. 



3113. Levelling Instrument with Telescope, 40 cm. long, 

 arranged for rotation and reversal in its sockets, with stand. 



A.. Bonsack, Berlin. 



The bearers are closed by springs. The horizontal circle is divided on 

 silver to |, and adapted for reading to one minute. 



3114. Compensation Level. 



F. W. Breithaupt and Son, CasscL 



A portable instrument. It possesses the important advantage that, without 

 previous correction, even if the telescope-cylinders are'unequal, correct levels 

 may be obtained, provided that the spirit-level is correctly adjusted, which 

 may be easily ascertained by turning it round in its points of suspension. 

 By means of the tangent screw the spirit-level is brought to equilibrium 

 in both positions of the telescope, and the mean of the two readings^ taken. 

 By this operation all errors are compensated. The divided head of the tan- 

 gent screw serves at the same time for distance-measurement ; and, besides, 

 a distance measure on glass is inserted in the eyepiece of the telescope for 

 direct measurement. 



3116. Levelling Instrument of Precision, with telescope 

 of 15" focal distance, 1*6" aperture, a so-called Compensation 

 Level with rotating water-level, according to new patent con- 

 struction. Ott and Coradi, Kempt en, Baviera. 



3117. Levelling Instrument with horizontal circle. 



Imperial German Navy (August Lingke and Co.). 



3122. Large Reversible Level, for precision levelling. 

 Length of the telescope 0'50 m., magnifying power 36, 65 diame- 

 ters, in steel sockets, with reversing level of exactly equal tangents, 

 indicating five seconds, latest construction. Ed. Sprenger, Berlin. 



Length of telescope 0-44 meter, magnifying power 40 times, with a new 

 construction of double spirit-level in one individual of exactly equal tangents, 

 by which the employment of the second position of the telescope is greatly 

 facilitated, and the instrument works with great precision, as any inequality in 

 the bearing rings of the telescope immediately becomes visible. The support 

 with the bearers is of cast steel in one piece, and to protect it from rust is 

 coated with chloride of platinum. From this construction the instrument has 

 great stability. The object glass, eyepiece, and field glass are removable, 

 so that the telescope is free from optical errors. The bearing rings of the 

 telescope are of aluminium-bronze, and there are removable distance-threads. 

 40075. 3 B 



