638 SEC. 15. GEOGRAPHY. 



3119. Large Levelling Instrument, with folding down 

 telescope and attached water-level, adapted for very fine measure- 

 ments ; ether-level with air chamber ; the objective 36 mm. aper- 

 ture, and 40 cm. focal distance. A. Frerk and Son, Hanover. 



30 2O. Medium Levelling Instrument, with fixed telescope 

 objective, 27 mm. aperture and 33 cm. focal distance ; ether-level ; 

 above it, a reflector. A. Frerk and Son, 'Hanover. 



3121. Small Levelling Instrument. Objective 15 mm. 

 aperture, 20 cm. focal distance. A. Frerk and Son, Hanover. 



3122. Large Reversible Level, for precision levelling. 

 Length of the telescope 0'44 m., 36 times magnifying power, in 

 steel sockets, with reversion level of exactly equal tangents, indi- 

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



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

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

 })y 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. JFrom this construction the instrument has 

 great stability. The object glass, eye-piece, 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. 



3123. Large Reversible Level, for precision levelling. 

 The telescope 0-36 m. in length, magnifying power 28 times, in 

 all other respects like the previous one. Ed. Sprenger, Berlin. 



3124. Universal Instrument, by Breithaupt and Son. 



Royal High School of Industry at Casscl. 



Universal Instrument, with distance-measurer for levelling and measuring 

 horizontal and vertical angles. This instrument is intended for large surveys 

 and levellings, which require to be performed with great accuracy and as 

 little expenditure of time as possible. It corresponds with the tacheometer, 

 but exceeds this in the amount of work that can be got through with it. The 

 telescope rests with prisms and screw-heads upon the steel plates of a bearer, 

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

 head of the axis serves for accurate perpendicular position. Horizontal circle, 

 with glass coverings to the verniers. Constructed in 1854 by F. W. Breit- 

 haupt and Son. 



3125. Levelling Instrument, for folding down, by Breit- 

 haupt and Son, in Cassel. 



Royal High School of Industry at Cassel. 



The telescope and the spirit-level, as in No. 1 arranged upon prisms, screws, 

 and steel plates for reversal and distance-measuring. This arrangement, ful- 

 filling the same purpose as the cylinder on the telescope, has the further 



