OBJECTIVES CONTINUED. 



light, superlatively corrected as they are, enable them 

 to be used under wonderfully high eye-piecing, and 

 with comparatively slight loss of either light or defini- 

 tion, while by the aid of these high oculars, the greatest 

 magnifications are obtainable, and in these particulars 

 also, do these objectives again stand alone and defiant. 

 ' Somehow, among the few who have paid attention to 

 the claims of the balsam apertures, it has got to be the 

 popular impression that it is the particular province of 

 these objectives to bear high oculars, the impression 

 having force in a restricted, or limited sense to wit, 

 that there is nothing gained really by the use of highi 

 balsam angles under low or medium oculars. 



Any idea of this sort is totally in error, for even 

 under a low or medium eye-piece, the higher balsam 

 angle will demonstrate its presence by an increase in the 

 intensity ot definition, while its greater power of light 

 is in itself & power capable of being turned to certain 

 necessary and useful purposes. I have already stated 

 that it is quite possible to distinguish the one glass 

 from the other, and, I might have added, " under low 

 or medium oculars." 



But, as I have said, with all this gain, there is an ac- 

 companying loss of working distance. But this is not 

 all; those who have been accustomed to work all their 

 lives with objectives of low or medium apertures, might 

 with good reason, claim that the high balsam angles 

 are " exceedingly inconvenient to use." Palpable is 

 the fact, that the slightest error in the collar adjust- 

 ment, or in the management of the illumination, will 



