754 SEC. 15. GEOGRAPHY. 



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. 



3125. Levelling Instrument, with rotating and reversing 

 telescope, by Breithaupt and Son, Cassel. 



Royal High School of Industry, Cassel (W. Narteii). 



The telescope and the spirit-level, as in No. 3124 arranged upon prisms, 

 screws, and steel plates for reversal and distance-measuring. This arrange- 

 ment, fulfilling the same purpose as the cylinder on the telescope, has the 

 further advantage that any wearing that may be produced by the screws may 

 be at once corrected without the aid of the mechanician. The instrument is par- 

 ticularly adapted for levellings of precision ; that now exhibited was employed 

 in this way in the European measurement of a degree by Prof. Spangenberg. 



d. QUADRANTS AND SEXTANTS. 



3083. Quadrant, of boxwood. One side engraved as usual, 

 on the other are numerous figures and a movable index. 



William Sykcs Ward. 



3084. Gunter's Quadrant, of boxwood. 



William Sykes Ward. 



3085. Quadrant, of brass ; one side divided as a geometrical 

 square, the other with movable circle and index, signs of the 

 zodiac, and various figures. William Sykcs Ward. 



3O67. Sextant of Aluminium, constructed by A. Petri, 

 Rostock. Prof. H. Karsten, Rostock. 



3085a. Jacob's Staff, made to take astronomical observa- 

 tions, with double arcs ; 17th century. 



Ministry of Marine, Madrid. 



3085b. Surveying Instruments of the 18th Century. 



Ministry of Marine, Madrid. 



3085c. Two Double Sextants, made in the last century by 

 Davis. Ministry of Marine, Madrid. 



3031. Double Pocket Sextant, an instrument for travellers. 

 Made by H. Porter. Capt. C. George, R.N. 



It can be used on shore with artificial horizon, in obtaining altitudes near 

 the zenith ; also as two single sextants, one of which can be used in case of 

 the other being damaged ; or one can be used by an assistant, and the other 

 retained by the observer. 



It can measure angles of nearly double the arc which can be measured by 

 the ordinary sextant. 



It can be used for the simultaneous measurement of two angles in the 

 same place. 



For laying out curves for railways and harbours, it is invaluable to the 

 civil engineer and marine surveyor. 



