398 F. K Wright— Bi-quartz Wedge Plate. 



until the illumination of the two halves of the Lippich polarizer 

 system is the same. After the introduction of the sugar 

 solution, the quartz compensator is inserted until the original 

 equal intensity of the halves is restored and the angle of rota- 

 tion derived directly from the compensator scale. 



This being the case, it would considerably simplify the con- 

 struction to allow the analyzer to remain rigidly fixed and to 

 revolve the two nicol prisms of the Lippich polarizer system, 

 thus eliminating the complicated gearing of the Bates polar- 

 iscope, which mechanically is an exceedingly difficult piece of 

 apparatus to construct and to operate without lost motion. The 

 revolution of the polarizing prisms in equal and opposite angles 

 can be accomplished either by means of the worm thread device 

 adopted in the binocle ocular of h*g. 11 of the preceding article, 

 or by a grooved arm into which pins connected with the sup- 

 porting collars of the nicols fit and slide as the arm is inserted. 

 Mechanically these devices are not difficult of construction and 

 the angle of revolution can be read off accurately. 



In the foregoing pages the bi-quartz plate wedge is suggested 

 as a simple and effective basis for the construction of a polar- 

 imeter of adjustable sensibility in which the error from the 

 asymmetry of the Lippich system, together with all the serious 

 complications of mechanism, are completely avoided without 

 loss of accuracy. Such a plate has been constructed and 

 successfully applied to the exact location of crystal extinctions, 

 but unfortunately pressure of other duties has prevented the 

 writer from actually constructing a saccharimeter. Through 

 the courtesy of Dr. Bates of the Bureau of Standards, however, 

 an opportunity was given to test the wedge on a large and 

 accurate standard polarimeter illuminated by homogeneous 

 green light from a mercury quartz-glass arc. Its performance 

 was entirely satisfactory, minute displacements of the analyzer 

 from its position of true extinction being readily detected. 



Geophysical Laboratory, 



Carnegie Institution of Washington, 



Washington, D. C, July 6, 1908. 



