140 PROCEEDINGS OF SOCIETIES. 



from the object, and sends them on to assist in the formation of a 

 more perfect image in the eye-piece. In short, the water becomes an 

 integral part of, and a new optical element in, the combination, and 

 doubtless assists in the removal of residuary secondary aberration in 

 the lens. In awarding praise to the immersion system, I by no 

 means intend to disparage the dry objective ; I am convinced, how- 

 ever, it is to the immersion objective we must look for increased power 

 and usefulness in histological work. I am glad to acknowledge that 

 hitherto I have been quite content to employ what may now be called 

 our old half-inch and a quarter, made by Andrew Ross more than 

 twenty years ago ; neither having a greater angle than 75°. Lately, 

 I have used a \ by Dallmeyer (Andrew Ross's son-in-law), the angular 

 aperture of which is 120°. The excellent workmanship of this optician 

 is well known and recognized, both on the Continent and in this 

 country, and therefore needs no praise from me. I must, in justice 

 to Mr. Dallmeyer, say that his \ objective works through almost any 

 thickness of cover-glass, and its aberrations are equally well balanced 

 for uncovered objects. It bears the highest power eye-piece, and gives 

 a magnification of 1000 diameters in every way satisfactory ; this 

 perhaps, after all, is one of the best tests of a good objective. It 

 proves beyond a doubt whether the angular aperture of the objective 

 is brought to the maximum of utility, and increases its value in the 

 eyes of the pathological microscopist. 



To enter, however, into the history of the discoveries and improve- 

 ments which each has effected, or to assign the share of honour which 

 each labourer has reaped in this ample field, forms no part of my 

 present discourse. In the language of Herschel, — " of the splendid 

 constellations of great names which adorn the history of the micro- 

 scope, we admire the living and revere the dead far too warmly and 

 too deeply to suffer us to sit in judgment on their respective claims or 

 merits ; to balance the mathematical skill of one against the experi- 

 mental dexterity of another, or the philosophical acumen of a third, is 

 scarcely possible. So long as one star differs from another in glory, 

 — so long as there shall exist varieties or even incompatibilities of 

 excellence,— so long will the admiration of mankind be found suffi- 

 cient for all who truly merit it." 



