II. LENGTH. 57 



vertically, the water-level turning thereby between its points. If after the 

 proper attachment the bubble deviates from the centre, half of this deviation 

 will be corrected by the regulating screws of the tripod, and the other by the 

 said correction arrangement a. It is, however, to be mentioned that previous 

 to the above proof the parallel position of the water-level axis towards its 

 points of attachment is to be examined, which can effected by reversing 

 between its two points, and thereby a deviation of the bubble, if there be any, 

 will be removed half by the adjusting screw 6, and the other half by the 

 arrangement a. Finally, there remains the examination and correction of the 

 water-level sideways to be made, which is done in the usual manner by the 

 screw c. This attaching or adjusting water-level may also be recommended 

 for other purposes, for instance, in mounting of machines, &c. 



Regarding the peculiar construction of the aforesaid adjusting water-level, 

 the suspension between two points, in general, it may be remarked that the 

 same has been derived from the compensation-level constructed by F. W. 

 Breithaupt and Son some years ago (vide Dingler's Polytechn. Journal, 

 vol. CLIV. p. 401). In what manner this principle has been adopted by other 

 mechanical workshops, and represented partly as an invention of their own, 

 has been proved by an article in this Repertorium, vol. IX., p. 127, by the 

 addition of an arrangement or simplification totally at variance with the 

 construction. 



E. DIVIDING ENGINES. 



248. Instrument for dividing Mathematical Scales or 

 Rules. 



Lent from the Patent Office Museum by the Commissioners 

 of Patents. 



This instrument is to be used for dividing scales according to the French, 

 Swiss, or English measures of length, and is provided with a vernier for 

 obtaining the smaller divisions of the scale. It can also be adapted for 

 producing diagonal scales. 



265. Machine for dividing right lines, by Nicholas Fortin. 



MM. Fortin Hermann Bros., Paris. 



This machine is that constructed by the celebrated inventor in 1787, and 

 used in the works connected with the adoption of the metrical system. 



The pitch of the screw is exactly one millimetre. (Fortin's machine for 

 dividing circles, as well as this machine, was presented to the Conservatoire 

 des Arts et Metiers by MM. Fortin Hermann Bros., in 1876.) 



297. Micrometer Dividing Machine. 



Voigt and Hochgesang (Gust. Voigt\ Gottingen. 



The screw of the dividing machine has a rising gradient of mm. to 

 0*25 mm. The top of the same is divided into 200 parts ; each part, there- 

 fore, corresponds to -gfa millimeters. The nonius supplies a reading of 

 -J^ of this value. By a spring fixed in the inside of the prism the dead 

 movement of the screw will be completely removed. 



The tracing appliance is constructed in the simplest manner possible. The 

 tracing point a diamond is lifted by a mechanical contrivance, and let 

 down again. 



The sledge allows of drawing a line of 30 millimeters in length. 



For constructing ocular micrometers there is an arrangement making three 

 linear lengths in a mechanical manner. 



