The President's Address. By the Rev. W. H. Ballinger. 183 



to which our Joumal has been brought. The whole compass of 

 such special or collateral knowledge as any of us may desire to 

 reach, is either summarized or indicated for us there. Eemembering 

 this, I shall call your attention to a study I have been able to make 

 of the life-history of a septic organism which I beheve is hitherto 

 new to science. 



Some four years have been embraced in completing the work, 

 and I have had the advantage of the very best and finest lenses 

 which our recent advances in the theory and practice of the con- 

 struction of high-power lenses have afforded. 



I may remark, however, that for all work of the class I am 

 about to detail, it is absolutely needful that, for continuous research, 

 an air lens of high power should be used. You are well aware that 

 both oil and water, as immersion media on the surface of the deli- 

 cate cover, imperil, every moment, the fluid heneath the cover, 

 and within which the subject of investigation is in constant 

 motion. 



For this continuous work I rely on a 1/16, of great merit in 

 all respects, as an air lens ; on a 1/25, which has very fine quali- 

 ties; and on a 1/50, which greatly surpasses, in all the qualities we 

 seek, a lens of the same power by the same makers used up to four 

 years ago. 



The lens, however, on which I still rely chiefly for this work is a 

 1/35, which for an air lens possesses qualities of the highest order. 



But beyond the work of continuous watching, when the oppor- 

 tunity presents itself, there is the work of developmental mor- 

 phology, of discovering all the details of the adult form, and of 

 thoroughly demonstrating the changes that ensue in the completion 

 of a Hfe-cycle. 



It is here that first, water immersion, and now, above all, 

 homogeneous lenses have been to me of untold value. 



Happily I have no need to deal with, even in review, the 

 mathematical laws of aplanatic combinations, nor the diffraction 

 theory of microscopic vision, and all that attends it, on which this 

 vast improvement depends. In that I have been anticipated by 

 competent masters. 



But I ought to yield to none in the sense of obligation under 

 which I rest for such splendid optical advance. With these new 

 lenses I have gone over again all the critical parts of the work 

 which I have had the honour from time to time to present to this 

 Society, and others; and although I have discovered no error of 

 interpretation, I have been compelled to see that many of the deli- 

 cate points of detail, discoverable only by the most persistent effort 

 and carefal manipulation then, could be demonstrated with com- 

 parative readiness now. 



The benefit arising from their use in the study I am about to 



