52 SEC. 3. MEASUREMENT. 



247. Measure of Length, according to natural principles. 



Hans Baumgartner, Basle. 



250. Half Metre, maple, with points. 



Geneva Association foi* the Construction of Scientific In- 

 struments. 



251. Brass Metre. (Grand Duchy of Baden Model.) 

 Geneva Association for the Construction of Scientific In- 

 struments. 



252. Steel 2-Metre Standard, with points. (German 

 Model.) 



Geneva Association for the Construction of Scientific In- 

 struments. 



253. Brass Standard Metre. (Swiss Model.) 



Geneva Association for the Construction of Scientific In- 

 struments. 



The Geneva Association for the Construction of Scientific Instruments 

 possesses in its laboratories a machine for the division of straight lines, to 

 the construction of which it has endeavoured to apply all the improvements 

 of modern science. These efforts have been crowned with success, and the 

 increasing reputation of this machine, which may be considered as the most 

 complete at present existing, has obtained for the Geneva Association orders 

 for metrical standards from several European Governments. 



The machine is worked automatically, that is, all the process of dividing is 

 done mechanically. Thus, apart from the inaccuracy consequent on the tem- 

 perature of the operator, it avoids the errors proceeding from inattention 

 or fatigue on his part. Mechanical action has, moreover, the advantage of 

 being more regular, seeing that the motive power is always equal. 



An ingenious contrivance enables the correction of errors due to a change 

 of outward temperature during the process of division, to be effected ; thus, at 

 any temperature a correct graduation corresponding to is obtained. By 

 the same means, a division of any length may be made, although the pitch 

 of the thread of the screw of the machine, and the length of the division re- 

 quired, may be incommensurable. 



The pitch of the screw has been thoroughly examined and corrected, so as to 

 guarantee accuracy to the -^^ of a millimetre. 



This machine for dividing straight lines has been used to effect the normal 

 division of the large machine for dividing circles which stands by its side on 

 the same bed of concrete. This application has been the means of exactly 

 ascertaining the coefficient of dilatation of the machine for dividing straight 

 lines. The maximum of error found in the division of the normal circle was 

 less than a second. It is impossible to expect greater accuracy when it is 

 remembered that the arc of a second on the circumference of the divided 

 circle represents about -^^ of the millimetre. 



259. Standard Metre, with rack motion to be used as a 

 machine for dividing other metres. 



Geneva Association for the Construction of Scientific In- 

 struments. 



