99 



the objectives centered and adjusted for focus, or 

 nearly so, which is a very decided consideration. 



Fig. 20. 



The same advantage holds good for the triple nose- 

 piece in the case of three objectives, or the quadruple 

 nose-piece for four. In these it is usually not con- 

 venient to arrange the objectives to correspond in 

 focus on account of the considerable difference in 

 focal distance. 



The next in order of demand is the Abbe conden- 

 ser in its various forms of mounting. While some 

 able microscopists hold that the proper use of the 

 mirror will satisfy every demand, and that unless 

 properly used the condenser is disadvantageous 

 instead of beneficial, it is unquestionably true that it 

 will give results which the mirror alone can not pro- 

 perly give. Furthermore it enables results to be 

 obtained easily, which would require careful and long 

 experience by the mirror. The writer is in the best 

 position to know from the many inquiries received 

 from professional men, on how to increase the light, 

 that for this purpose and the better distinguishment 



