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The Ordinary Condenser Improved, or " Circular" 

 Illumination Superseded. 



By W. K. Bridgman, L.D.S. 

 (Bead May 25, 1877.) 



During the working out of the mechanical arrangements for the 

 " reflecting illuminator," it was very soon discovered that no incon- 

 siderable portion of the superiority of its illuminating effects was 

 derived from conditions equally applicable to almost every other 

 form of condenser ; and which could be adapted to most, if not all, 

 of those already existing, so as to give to the majority of objects, 

 commonly seen with the medium and lower powers, but more 

 especially such as were dependent on stereoscopic effect and the 

 total absence of haze or glare, a clearness and distinctness of detail 

 very far in advance of what is obtained in the ordinary way. 



With the highest powers it is well known that almost every- 

 thing depends on the illumination ; this being the chief diffi- 

 culty, as the very slightest variation may either make, or wholly 

 mar, the effects. In proportion, however, as we descend in the 

 scale, so does this great nicety of adjustment seem to be less needed ; 

 and with a very large proportion of observers, so long as there is 

 light enough, and that not too overpowering, little further is heeded. 

 But let an equal amount of attention be paid to the illumination for 

 the lower powers as for the higher, and the result will be found 

 amply to compensate for any extra trouble it may involve. 



Let some well-outlined object be placed under one of the medium 

 powers, and be illumined with direct light, or light thrown up 

 centrally with the optical axis, and it will go in and out of focus 

 with a hazy outline expanding equally in all directions. 



But let the mirror be turned to one side so as to throw the light 

 obliquely across the object, and the outline will then expand only on 

 one side, and that in the opposite direction to the course of the 

 illumination. 



2 B 



