408 F. E. Wright — JVeto Petrographic Microscope. 



Fig. 1. 



Fig. 1. New petrographic miseroscope. T, rigid bar connecting two 

 nicols and effecting simultaneous revolution of the same ; A, arm connect- 

 ing upper nicol carriage with T ; C, part supporting bar T and revolving 

 about stage : B, arm from lower nicol carriage connecting with bar T ; by 

 means of the screw and cross plate at B, this arm can be instantly released 

 from T and the lower nicol either revolved by itself or, after a release by a 

 snap spring not shown in the figure, thrown out of the field altogether. The 

 total angle of simultaneous revolution of both nicols by this device is 190°. 

 0, new mechanical stage, simple in design and construction and fairly 

 dust-proof. Hi, stage screw with divisions on head reading to •01 mm 

 motion of stage plate. Q, sensitive-tint plate inserted above lower nicol, W, 

 and revolvable about microscope axis by means of containing carriage, F. 

 M, combination wedge above objective ; a x a 2 , fine adjustment screws above 

 objective ; U, screw of fine adjustment device of upper microscope tube ; V, 

 iris diaphragm below Bertrand lens, diaphragm opened and closed by turning 

 head V, which is connected with iris diaphragm by pin and ratchet move- 

 ment; E, pin for insertion of Bertrand lens which moves in an accurately 

 fitting carriage, supporting iris diaphragm V, Bertrand lens E and auxiliary 

 lens L, which swings on an arm indicated in fig. la and is of such focal 

 length that together with ocular, it forms a small microscope used in 

 focusing the image from the objective in the plane of the iris diaphragm, 

 V. The supporting carriage of V, E, and L, can be moved up and down in 

 the microscope tube and the amount of movement read off on the adjacent 

 scale, thus obtaining different magnifications (6*5 to 15*2 diameters) of the 

 interference figure. G, upper iris diaphragm directly beneath ocular. 



