258 Immersed Ajpertures. 



a 'score of years ago. But after all, what admissions am I now 

 expected to make ? I first controverted the preposterous assertion, 

 that more aperture was gained by immersion, as the fluid was 

 alleged to admit extra rays, erroneously taken from an assumed 

 radiant point, quite regardless of their ultimate destination ; and the 

 further statement, that there was no loss of aperture by using an 

 ordinary object-glass as an immersion. 



Suggestions and possibilities of doing this by peculiar means 

 (such as I had already used) never entered into the early phase of 

 the question, or they would then have been met by me. 



Concerning the five or more degrees to be obtained in excess of 

 the 82° of an ordinary object-glass, 1 will say nothing till I have 

 witnessed some actual facts, forewarned by Dr. Woodward's sentence, 

 to be " cautious in describing objectives he has not seen." Extra 

 rays might possibly be accounted for in several ways. At present 

 evidence is required in order to demonstrate their position and 

 value in the micro-objectives under question ; till this is laid down 

 I am unable to make any concession on theoretical grounds. 



I must finally protest, in consequence of the allusion to the 

 glass forwarded to me for the measurements of the relative air and 

 immersed apertures. Across the Atlantic I have been universally 

 condemned for this, and without exception held to be " quite in the 

 wrong." I really cannot see how I am to blame in the matter. 

 The object-glass was not professedly an immersion one, and I had 

 no pretence for altering the adjustment to suit this unnatural con- 

 dition. Had I tampered with the adjusting collar during the trial, 

 no end of insinuations could have been brought against me for 

 " trickery." I did what I considered right for proving a question 

 of relative loss of aperture in balsam. I should have been quite 

 content to try it, if the adjusting collar had been pinned fast by 

 the senders in any position that they thought gave the desired 

 definition, or to have tried it with one of the Continental xV^hs, 

 such as are set to an average thickness of cover, without any 

 adjustment at all ; then this unhappy adjustment imputation could 

 not have been raised. I am at length told that the object-glass 

 defines best with a cover ytrth thick. Had I been previously 

 informed of this, I certainly would have got a Podura specially 

 mounted with this thickness for the occasion, as nothing of the 

 kind is prepared for sale in this country. 



To all these points I have before replied to the same efiect. 

 The controversy has been so long and tedious, that it is not a matter 

 of surprise that they should be forgotten. 



