enter without any friction and still tit so closely that it 

 drops slowly into its place from the compression of air 

 in the tube when the objective is attached. 



In the course of time a film is apt to form on the 

 surfaces <sf lenses, which will cause indistinctness in the 

 image. It is advisable to periodically unscrew both eye 

 and field lens from the mounting and carefully wipe 

 the inner and outer surfaces. In conclusion it may be 

 said in a general way that the layman has rarely the 

 fundamental knowledge and sufficiently long experience 

 to judge critically of imperfections which may exist. 



The idea is quite prevalent that there is a wide 

 variation in objectives of the same type from the same 

 maker. While this is quite true as between objectives 

 of different makers and also of makers whose pro- 

 cesses of production have remained the same as those 

 of former years, it is not so with the products of those 

 progressive firms who by common consent stand at the 

 head in their respective countries. Precise and delicate 

 as the various stages of production are, rigid control 

 and inspection removes all personal factors and elimin- 

 nates all chance in the final result. We do not mean to 

 argue that the work of the best should be unquestioned ; 

 on the contrary, it is advisable to examine all work 

 critically, and preferably by comparison, and we are 

 sure progressive makers will welcome all efforts in this 

 direction and will lend their aid to a more intelligent 

 use of their products. 



