632 SEC. 15. GEOGRAPHY. 



carriage 4 metres in length, and compared iu order with the intervals of 

 the measuring rod divided into metres. For this purpose the carriage is 

 moved to and fro upon the base piece under two microscopes placed upon a 

 common bearer. This bearer may be pushed along the whole length upon 

 the base piece (like the standard metre upon the carriage). In the second 

 case the two measuring rods are laid side by side upon the carriage, and 

 compared under the microscopes, one of which is attached to the common 

 bearer, and the other to a special arm of the base piece at a distance of 

 4 metres from the former. The comparator is also arranged, if the purchaser 

 \vishes it. for the comparison of the standard metre (a traits) with a yard 

 end measure (a bout). For this purpose small cylinders with scales are applied 

 to the standard yard in order to compare suitable portions of these scales with 

 the metre ; then the sum of the lengths of the cylinders up to the portions of 

 the scale employed is found by putting the two together directly. The whole 

 comparator is to be enclosed in a wooden case, in order to keep the measures 

 at an equable temperature. 



3101. Geodetical Tachygraph, a representation of an in- 

 strument invented and constructed by the exhibitor, for conducting 

 measuring operations in their minutest details. 



Professor Joseph Schlesiuger, Vienna. 



This instrument consists of a circle with divisions, mounted in a movable 

 frame, that can be adjusted so as to place the circle in any given direction. 

 It is also provided with a rule to draw angles. 



3102. Eckhold's Omnimeter, for measuring linear distances 

 by one and the same operation. Elliott Brothers. 



This instrument is a transit theodolite, with an apparatus for measuring 

 by one operation the distance of an object or staff of a determined length, 

 and its height over or under the level line of the instrument ; the former with 

 the accuracy of a good chaining, the latter with the precision of a perfect 

 levelling, and accomplishes the work of theodolite, level, and chain with a 

 great economy of time. 



3103. Apparatus for Determining the Exact Time of 

 an Earthquake. (Seismochronograph.) 



Royal University at Breslau, Prof. Dr. Lasaulx. 



3104. Abney's Level. The instrument was designed by Capt. 

 Abney, R.E., for military reconnaissances. It measures vertical 

 angles by means of a spirit level attached to a graduated arc, which 

 is capable of moving round an axis. The object whose angle of 

 depression or elevation is to be ascertained, is brought into the 

 field of view, and the spirit level is then moved till the bubble is in 

 the centre. When in this position the bubble is seen in a reflector 

 placed in the body of the tube ; an opening being left for the 

 purpose. Elliott Brothers. 



3105. Elliott's 14-inch improved Dumpy Level, with com- 

 pass for taking levels and bearings. Elliott Brothers. 



This instrument, being provided with an object glass of large aperture and 

 short focal length, and sufficient light being thus obtained to admit of a 



