THE MICROSCOPE. 31 



opticians should have, for so long a time, sacrificed this 

 primary consideration to the far less important one of occa- 

 sionally fitting a large achromatic condenser below the stage. 

 When the pillar of the microscope is bent, the glass slip 

 must be prevented from sliding down the stage. Nothing 

 does this so simply and so efficiently as a pair of clips made 

 of brass, below which the ends of the slip are placed. A 

 movable brass ledge sometimes is placed across the stage to 

 serve instead of these clips ; but a simpler contrivance for 

 wasting one's time could scarcely have been devised. Movable 

 stages are lauded by some j those with screws are scarcely 

 worthy of serious attention, but the stage moved by a lever 

 with a ball and socket joint, devised by R. and J. Beck, is 

 if a movable stage be desired a good arrangement. At 

 the same time, however, it is, I believe, much better to learn 

 to do without any movable stage unless for very exceptional 

 work under very high powers ; in that case it is useful to 

 those whose fingers have not acquired the necessary amount 

 of dexterity to move the glass slip carefully. Nothing is so 

 convenient as the motion communicated directly to the glass 

 slip by the fingers. If the stage be kept smooth and clean 

 and a polished glass surface to the stage is on this account 

 the best the slide can be readily moved in any direction, 

 and when working with very high powers it is only necessary 

 to put the slip under the clips to keep it from moving too 

 easily. With a little practice it is remarkable what a 

 delicate movement may be given by the fingers. 



The////<zrof the microscope should be flexible, in order 

 that the head may be kept in the erect posture, a condition 

 that greatly diminishes the fatigue of a day's work. When 

 working with fluids, the stage has of course to be made 

 level. It is important to see that the hinge of the pillar be 

 thoroughly well made, otherwise the stage will be unsteady. 



The telescope tube holding the ocular and the objective 

 has been already alluded to ( 41). 



A nose-piece (Fig. 3 2) is an excellent device for saving 

 time in changing from one objective to another. In this 

 simple contrivance, devised by Mr. Brooke, the low and 

 high lenses are screwed to a framework which can be 



