162 THE AMERICAN MONTHLY [June, 



affords so admirable a description of the improved in- 

 strument, which has been constructed for him by the 

 well-known Berlin crystallographical optician, Herr 

 Friess, and likewise of the mode of employing it in con- 

 nection with the immersion method, that all will be in- 

 terested in it. Unfortunately the illustrations of Klein 

 cannot be reproduced. 



The microscope should be one of the petrological type 

 fitted with the usual accessories for the examination of 

 crystals in parallel and convergent polarized light. The 

 particular instrument constructed for Prof. Klein is 

 somewhat similar to the largest Friess model. It is so 

 arranged with respect to the centre of gravity that it 

 can be rotated into the horizontal position whenever de- 

 sired, a point of some importance with regard to the use 

 of an immersion liquid. The stage is circular and di- 

 vided so as to read with the aid of a pair of verniers to 

 single minutes ; it is further provided above with two 

 graduated rectangular traversing movements, one of 

 which is supplied with a micrometer registering 0.01 

 mm., while the other is capable of much more rapid mo- 

 tion. The advantages of the simultaneous rotation of 

 the polarizing and analysing nicols, as adopted in the 

 microscopes made by Mr. Swift under the direction of 

 Mr. Allan Dick, have been so well aj)preciated by Prof. 

 Klein that this has been arranged for in the new Friess 

 instrument. The carriers of the nicols are each furn- 

 ished with a toothed flange capable of gearing with a 

 small pinion, and the two pinions are arranged at the 

 ends of a connecting rod furnished at a convenient 

 height near the upper pinion with a milled flange by 

 means of which rotation can be eff"ected. Provision 

 is made for the lengthening of the connecting rod when 

 the focussing of the microscope by the rack and pinion 

 or by the fine adjustment is efl"ected, and care is also 



