96 REPORTS OF INVESTIGATIONS AND PROJECTS. 



The methods based solely on extinction angles for different faces are 

 inaccurate and unsatisfactory, chiefly because of the undue influence of small 

 differences in extinction angle on the resulting optic axial angle. 



In addition to the double-screw micrometer ocular, several new appliances 

 are described — an improvement of the Fedorow-Fuess universal stage, a new 

 form of condensor lens system, and a disk-shaped type of the Becke drawing- 

 table. 



(8) Potentiometer installation, especially for high-temperature and thermoelement 

 work. Walter P. White. Phys. Rev., 25, pp. 334-352, 1907. 



A fairly complete description of the methods of making the electrical meas- 

 urements of temperature regularly in use in the laboratory up to 1,600°, with 

 a discussion of the character and magnitude of the errors involved, the treat- 

 ment of leakage, etc. 



