188 THE president's address. 



diatom, although I knew the feat to be well within the capacity 

 of the lens employed. Thinking that my failure was clue to the 

 exceptional transparency of the silex of my diatom, mounted 

 as it was in Styrax, I temporarily gave up the attempt. 

 Subsequently, however, on " building up " the slide, by cement- 

 ing to it another of equal thickness, so as to make the two slips 

 together equal to about ^V of an inch in thickness, I was rejoiced 

 to find that my difficulty had vanished, for the macrum was 

 resolved into " checks." To any one who is still sceptical as to 

 the necessity of adjusting the thickness of his glass slips to the 

 focal length of his condenser, I recommend this experiment as a 

 useful object-lesson. As a matter of fact I have decided to build 

 up every one of my test slides in the manner above indicated, and 

 in future I shall use none but carefully selected slides of proper 

 thickness for the mounting of test objects. 



Within the last few days I have been permitted, through the 

 kindness of a friend, to examine an achromatic condenser of 

 entirely new formula, computed by Mr. Conrady, of London, on 

 the oil immersion principle. It transmits an aplanatic cone of 

 about 1"35 N.A., and works through a fairly thick glass slide. I 

 have as yet had only one opportunity of examining this con- 

 denser, but it appears to me to be one of great promise ; it is 

 beautifully corrected spherically as well as chromatically, and 

 considerably increases the resolving power of wide-angled apo- 

 chromatics on fine-lined tests. I hope to see further developments 

 of the achromatic condenser, at the hands of this talented optician. 

 It now becomes a pleasing duty to acknowledge my personal 

 indebtedness to my fellow-members of the Club for the uniform 

 courtesy and support which I have received during the year of 

 office which terminates to-day. To our honorary secretary and 

 honorary treasurer especially my thanks are due, for it is to their 

 unstinted devotion, both of time and energy, to the affairs of the 

 Club that is due in very large measure its present condition of 

 usefulness and success. Our honorary editor, too, has given me 

 constant assistance and ad\ice ; and to his ability and sacrifice of 

 valuable time we are all indebted for the exemplary editing and 

 publication of our Journal. I beg also to tender my cordial 

 thanks to our honorary librarian, our honorary curator, our 

 honorary reporter, and to my other colleagues of the Council, for 

 their kindness and support during my past term of office. 



