766 SEg, 15. GEOGRAPHY. 



G. G. Starke's universal levelling instrument, with telescope and Stampfer's 

 surveying screw. 



H. G. Starke's Universal levelling instrument with telescope. 



I. G. Starke's Tachymeter. 



K. Polymeter, by Jahns. 



M. G. Starke's perspective index with turning water level. 



A. Description of Praetorius's table, according to Schwenter. 



3134a. Folding Alhidade or Sight- Vane, small size, for 

 rapid military surveys, with plane table with scales from -^Vu to 

 2 oto 77- -M-. Georges Sarasin, Geneva. 



This instrument is so constructed as to give, with an approximate exacti- 

 tude which in no w r ay hinders the rapidity of the work (notwithstanding the 

 reduced size of the instrument for portability), the measure of distances by 

 means of a micrometer, and with the optional assistance of an improvised 

 sight, the measure of inclinations by means of a clinometer furnished with a 

 vernier reading to five minutes, and consequently the measure of the differ- 

 ences of level, as well as a sketch of the horizontal lines on the ground, with 

 the aid of a calculating rule. It is possible to check any inaccuracies of cen- 

 tering by verniers diametrically opposite to one another, and by turning the 

 telescope end for end. There are also means of adjustment and correction. 



3134:b. Folding Alhidade or Sight-Vane, large size., for 

 topographical surveys, with plane table to scales from ^^ to TTTJTJ o- 



3f. Georges Sarasin, Geneva. 



The plane table, constructed to give with considerable accuracy, notwith- 

 standing its reduced size for portability, measures of distances by the aid 

 of a sight stadia, inclinations by means of a clinometer furnished with a 

 vernier reading to three minutes, and consequently the measure of the differ- 

 ences of level, as well as a sketch of the horizontal lines on the ground, to 

 scales of from ^5- to ao'oo- It is possible to check any inaccuracies of 

 centering by verniers diametrically opposite to one another, and by turning 

 the telescope end for end. There are also means of adjustment and cor- 

 rection. 



3135. Signalling Apparatus ( Aeroclinoscope), by Major 

 Kromhaut. Prof. Buys-Ballot, Utrecht. 



This apparatus consists of four movable discs and two fixed hollow 

 cylinders. Two of the four movable discs never enter the space between the 

 cylinders ; the other pair remain constantly between the fixed cylinders, but 

 may very easily be placed in six different positions clearly to be distinguished 

 from afar. 



The two discs fi may be brought very easily close to one another and to 

 the first cylinder or the second cylinder ; or they may be more or less 

 separated, one close to one of the cylinders, or both or neither of them. We 

 have then six combinations. Each of the two other movable discs may be 

 hidden, also by another chord, by the cylinder next to it, or be placed close 

 to it or at a double distance. Three positions for each give nine combina- 

 tions (6x9 = 54). 



On the whole, when we make use of two pairs of discs we have 54 

 different signals, visible from far in a very distinct way. 



Now, in Holland, the upper outer discs are to represent the barometer- 

 height at Helder, Groningen, and the under outer discs the barometer-height 

 at Flushing and Maestricht, and these form at the same time the direction 



