The President's Address. By the Rev. W. E. Dallinger. 189 



eye-pieces I at that meeting expressed ; and need only add that since I 

 have become the possessor of a second object-glass of precisely similar 

 construction and power made by this firm, I am much strengthened in 

 the opinion I gave. 



We all appreciate the splendid services rendered to Microscopy by 

 Prof. Abbe; and it was a happy expression of that appreciation that 

 led Mr. Mayall to propose a visit to Jena, with his Microscope and such 

 object-glasses as he thought would worthily represent the standpoint 

 we had now reached in England. 



I understand that Prof. Abbe greatly desired this, wishing to possess 

 the fullest information as to our methods of testing object-glasses, and 

 to be permitted to examine our best optical work. 



I need hardly say that it was a source of great pleasure to me to 

 place at Mr. Mayall's disposal all the lenses and apparatus I possessed 

 that would serve him : for it was in the highest interests of the micro- 

 scopy of the world that so great a leader in its recent progress should see 

 the efiects of his teaching and practice as evidenced by our latest object- 

 glasses, and especially by the new apochromatic 1/12 by Powell and 

 Lealand, with its system of compensating eye-pieces. 



Mr. Mayall has told us the story of his visit ; of his kindly recep- 

 tion; of the earnest and repeated trials of the object-glasses he was 

 able to submit to Prof. Abbe, and of the frank appreciation expressed by 

 Prof. Abbe of the English object-glasses. This comparison will, in niy 

 judgment, *' make history " for the future of our instrument. It will 

 react here and in Germany. Prof. Abbe's splendid powers are more 

 than ever concentrated on the work of touching a higher perfection in 

 object-glasses, and he knows that every improvement initiated in Jena 

 will be watched by keen eyes in England; and he has evidence, which 

 will be as welcome to him as his work is to us, that we are not likely to 

 neglect any point of excellence, provided only we can be made to see it 

 as such. 



I understand that Dr. Zeiss admits that the formulae on which his 

 apochromatic objectives are constructed involve far greater technical 

 difficulties than were met with in the older formulae ; and this is 

 evidenced by the great number of separate lenses combined in the 

 construction. 



Now it has long been my judgment, and a judgment that has been 

 confirmed by men of large practical experience, that errors of technical 

 execution, when present, are shown at once by deep eye-pieces : with an 

 object of regular structure, whose image fills the field of the eye-piece, 

 the experienced eye readily detects a want of sharpness. I am bound to 

 say that the apochromatics from Jena did not impress me by this test 

 as having accuracy of technical execution equal to the object-glasses with 

 which they were compared. 



On the other hand, I find that with the new apochromatic made by 

 Powell and Lealand, I can employ advantageously, deeper eye-pieces 

 than I had ever used before. 



Now there is a less number of separate lenses in the London objec- 

 tive ; and whether this superiority is due to the less number of lenses, 

 or to other causes, I may not determine. I refrain from details con- 



