900 SUMMARY OF CURRENT RESEARCHES RELATING TO 



by Bulloch,* of Chicago, from Zentmayer's " Centennial " Micro- 

 scope.f 



The substage with centering movements fits on the first tail-piece 

 behind the stage, and is worked by rack and pinion. The mirror is 

 mounted on a crank arm on the second tail-piece. The tail-pieces 

 swing laterally either together or independently ; each is provided 

 with a graduated collar for registering the lateral rotation, and a 

 sprung-pin drops into a corresponding notch, fixing each in the 

 normal position when axial light is required. 



The stage is circular, and rotates about 7-8ths of a turn ; it has 

 goniometrical divisions near the edge ; " finders " are applied to the 

 mechanical rectangular movements. It is attached to the lower end of 

 the inclining column by a conical axis passing through and secured at 

 the back by a large milled nut. This stage can be removed and a 

 glass friction-stage substituted, which can be used reversed for 

 oblique illumination from the mirror, &c. The friction-stage is fitted 

 with a hemispherical lens so that its plane face is flush with the 

 surface of the stage as in Tolles's and other Microscopes. 



The focusing arrangements are of the usual Continental type. 

 A scale is applied on the side of the body-tube working against a 

 fixed vernier on the limb for recording focal distances by the coarse 

 adjustment, whilst for finer measurements a graduated disk is fixed on 

 the top of the column carrying the limb, and the fine focusing screw 

 rotates with an index pointer, by which the number of turns and 

 fractions can be registered. 



The body-tube is much larger than is usually adopted on the 

 Continent, and will admit an extra draw-tube (supplied with the 

 Microscope) for the Eoss gauge of eye-pieces. As arranged in the 

 figure there are two draw-tubes, the larger one sliding in the body- 

 tube and carrying the smaller, in which the Hartnack gauge of eye- 

 pieces is used. The " Society " thread is applied at the nose-piece. 



The suspension of the inclining column between the standards 

 appears to have been devised without regard to the balance of the 

 instrument. The trunnion axis is very nearly at the lower end of 

 the column, so that the stability of the position of inclination is 

 entirely dependent on the tension of the clamp-screws on the ends of 

 this axis ; if the unwary operator should loosen the clamp-screws 

 without supporting the column the optical part of the Microscope 

 falls forward or backward, in either case striking the table, as no 

 stop-pins are provided either to mark the vertical or the horizontal 

 position. 



The Microscope is manufactured by E, Liitz, and appears to us 

 to require thorough revision both in design and construction. 



Zeiss's Mineralogical Microscope. — This (fig. 162) is based upon 

 Dr. Zeiss's large Microscope-stand with the addition of a rotating 

 stage, polarizer and analyser, sliding quartz-plate above the objective, 

 and centering nose-piece. 



The polarizer turns away from the stage, as shown in the woodcut, 



* See this Journal, iii. (1880) pp. 1073-80. 

 t Ibid., pp. 1067-73. 



