THE POLARISCOPE AS APPLIED TO SUGAR ANALYSIS. 



to sacrifice the delicacy of the reading in order to obtain the passage of more 

 light, the accuracy of the observation being thereby increased. An instrument 

 using the Landholt- Lippich half shadow device, and in which the half shadow 

 angle can be varied at will, has been devised by Bates, and constructed by the 

 firm of J. and J. Fric. The analysing nicol and the polarizing nicol are 

 mounted in bearings, and are joined by gears with a connecting rod ; the gears 

 are controlled by the rotation of a milled head, and are such that the rotation 

 of the analyser is always twice that of the polarizer. A scale attached to the 

 milled head gives the half shadow angle. 



FIG. 239. 



The zero of the instrument is affected by a change in the half shadow 

 angle ; with an instrument adjusted for a half shadow angle of 10, the latter 

 may be varied from 4 to 12*4 with the introduction of an error of less than 

 1 Ventzke. Bates has worked out the corrections to be made for different 

 half shadow angles when the instrument is in adjustment for the latter equal 

 to zero, and this can be made practically instantaneously, the half shadow 

 angle being indicated as already mentioned. 



437 



