G14 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



means of a screw-clamp the pressure on the ball may be adjusted. 

 The tilting-stage is placed on the Microscope-stage, and the specimen, 

 roughly mounted on a glass plate 1 in. wide, is placed in the holder. 

 The apparatus is then adjusted so that the surface to be examined is 

 exactly at right angles to the optic axis. 



When the Microscope upon which it is used has a mechanical stop, 

 an adjustable plate may be placed at the base of the Microscope, so that 

 it may be used for temporarily fixing the long rod. In this case the 

 ordinary movements of the mechanical stage form a fine adjustment for 

 levelling the object. When the object is levelled the plate may be 

 released, and then the stage-movements arc used in the usual manner 

 for moving the object. 



(2) Eye-pieces and Objectives. 



Zeiss' A* Objective.* — This useful objective, in which there is an 

 arrangement for separating its component lenses by rotating a collar, 

 for the purpose of increasing its magnifying power, has had its 

 mechanism altered, so that now it is in its original form. 



When it was first introduced, the rotation of the collar caused the 



back positive lens to move away from the front negative lens, which was 

 fixed ; but in 1880 the motion was changed, so as to make the front 

 lens move while the back remained fixed.| The reason for this was, 

 that the back lens, in its excursion up the tube, should not foul the 

 diaphragm, usually placed by Messrs. Zeiss at the end of their draw- 

 tubes. Fig. 119, which is taken from this year's catalogue, shows that 

 Messrs. Zeiss have reverted to their original form in making the back 

 lens the movable one. 



An interesting account of the theory of this lens will be found in 

 the Journal for 1884, p. 450. 



Assorted Pairs of Objectives for Binocular Microscopes.:}:— These 

 are now supplied by Zeiss in a special form of setting, and mounted in 

 pairs on slides, and are well adapted for Greenough's binocular. They 



* Catalogue, English edition, p. 14, fig. 6. t Journ. R.M.S., 1880, p. 524. 

 ; Catalogue, English edition, 1902, p. 18. 



