44 Modern Microscopy 



It is asserted by users of Continental microscopes, whose 

 name is legion, that the British microscope exceeds the 

 needs of the laboratory worker ; the only response to such 

 a criticism from the expert is that there is a want of 

 appreciation and education in matters microscopical in the 

 laboratory. It is impossible to disregard the modern spirit 

 which demands excessive rapidity of work at the cost of 

 excellence and accuracy, and it is not too much to say that 

 the man who examines structures with a good yV-iiich oil 

 immersion objective and an Abbe illuminator has limited 

 his knowledge to an extent which would cause him great 

 surprise if he had but the opportunity of seeing the same 

 subject properly illuminated with a sub-stage condenser 

 having a suitable ratio of aperture to that of the objective 

 and the microscope properly manipulated. The defects of 

 the Continental microscope are in a large measure dimin- 

 ished because of this very restricted cone of illumination 

 which is yielded by the Abbe illuminator. 



The modern -j-V-inch objective having a numerical aper- 

 ture of 1*25 to 1"3 will bear a solid cone of illumination of 

 0*9, and when it is stated that the Abbe illuminator regularly 

 provided, not only by Continental opticians, but also by 

 English houses, only yields an aplanatic cone, under the 

 most favourable circumstances, of 0'5, it will become only 

 too' apparent how utterly restricted the laboratory worker 

 becomes in his work when outfitted with the apparatus 

 which the Continental optician provides. "When once the 

 Abbe illuminator is abandoned and a suitable well-corrected 

 condenser is substituted for it (for be it remembered the 

 Abbe illuminator is not even achromatized) it will become 

 necessary to improve the construction of the Continental 

 stand. Centring screws must be perforce provided to the 

 sub-stage ring; fine adjustments to the sub-stage, though not 

 indispensable, will soon be found desirable, and the inven- 

 tive faculty will quickly be brought into play for the provision 

 of a slower acting fine adjustment. As matters stand to-day 

 it is impossible to do other than advise that an English 



