340 SUMMARY OF CURRENT RESEARCHES RELATING TO 



tliat the marginal rays are not image-forming may be almost infinitely 

 varied. 



If these experiments cannot be made to bring out the desired 

 results, one thing is evident, the objectives that have been made use 

 of have not been properly corrected ! 



(7) " Only a Question of Nomenclature." — The last fallacy of 

 the angular aperturist, after he feels that his view is not so sound 

 as he supposed, is that the dispute has been " only a question of 

 nomenclature." 



Now we quite agree that in scientific discussions generosity to 

 fallen foes is no more out of place than it is in actual warfare, but, 

 nevertheless, we have always combatted this remark, because we have 

 had impressed upon us by the force of considerable practical experi- 

 ence that it has in the past largely contributed to obscure the fact, 

 which it is essential should be borne in mind, that the diiference in 

 the two views is in reality one of the highest importance, and one 

 which every person who works with the Microscope should appreciate. 

 The biologist and even the microscopist sees the controversy on 

 aperture end in the suggestion that it is " only a question of nomen- 

 clature," and he therefore comes to the conclusion that the whole 

 matter is one of perfect indifference as regards the practical use and 

 improvement of the Microscope. If English microscopists had only 

 been able to grasp the theoretical grounds on which wide-angled 

 immersion lenses are shown to have necessarily a larger aperture 

 than dry ones, there can be no doubt that we in England would have 

 been ten years ago where we are only to-day. 



" Only a question of nomenclature" is a phrase which has a well- 

 defined meaning, being applied to the case of discussions in which 

 there is agreement as to the essence of the thing which forms the 

 subject of discussion, the difference being only as to what it should be 

 called. 



Let us consider then whether the differences on which the aperture 

 theories are founded do or do not go to the essence of the matter, and 

 in this we will draw exclusively from the printed pages of the recent 

 discussion We confine ourselves to a few only, but we need hardly 

 point out that an exhaustive consideration would of course simply be 

 a summary of the whole of the fallacies to the exposure of which the 

 preceding pages have been devoted. 



(1) It was asserted and made the keystone of the demonstration 

 that the radiation of light in air was exactly the same as radiation in 

 water or oil, and that equal angles in different media represented equal 

 apertures. If that is only a question of nomenclature there can 

 never be a dispute on essentials. 



(2) To support the view contended for, it is supposed that the 

 plane surface of a lens exercises power, and that when that is 

 abolished there is a loss, which must be compensated for by increased 

 curvature at the spherical surfaces. This is a notion which not only 

 upsets all the principles of practical optical construction, but the 

 most settled — indeed, the simplest— laws of optics. Can it be said 

 that this is only a dispute over nomenclature ? 



