A Top Stop for the Microscope. By J. W. Gordon. 3 



cases the condenser beam is powerfully supplemented by rays in 

 some or all of these different ways originating in the object itself. 



It is easy thus to advance to a perfectly clear idea of what we 

 mean by illumination under a wide angle, but having done so, 

 we find that the next step lands us in uncertainty. For it is most 

 natural to ask concerning the broad wave-front built up in this 

 way of elements derived from the condenser and of other elements 



Fig. 1. 



Top stop fitting, with an inspection 

 lens in position. A. Loose cell 

 for carrying the stop. B. Pivot 

 on which the cell carrying arm 

 swings. C. Excentric for swing- 

 ing the arm to cause the stop to 

 traverse the heam in a transverse 

 direction. D. Propelling screw 

 for causing the stop to traverse 

 the beam in the fore and aft 

 direction. E. Supporting screw 

 for adjusting the height of the 

 stop. P. Removable gallery for 

 carrying the inspection lens (or 

 camera). G. Ring for mounting 

 the fitting upon the draw-tube of 

 the Microscope. 



Fig. 2. 



Top stop fitting, with camera 

 in position on the gallery. 



supplied by the object : Is it an individual thing having properties 

 different from the properties of its parts, or is it only an aggregate 

 endued with the total of all the properties which are proper to its 

 various constituent parts ? The question suggests a distinction 

 like that between a mixture and a compound in chemistry. A 

 molecule, which consists of atoms of oxygen and carbon, is an 

 individual thing having chemical properties wholly unlike those of 



B 2 



