728 Transactions of the Society. 



the older objective, particular attention being given to such as 

 possessed extremely elusive features just within the grasp of the 

 lens. In every case without exception the observations previously 

 recorded were confirmed by the new objective, features previously 

 extremely difficult being found comparatively easy. It should be 

 clearly understood that the new Zeiss apochromatic was manu- 

 factured with no intention of being employed solely on the Dia- 

 tomacese." Mr. A. M. Jones spoke next, and said "that at a 

 recent Meeting of the Koyal Photographic Society, Mr. Max Poser, 

 of Messrs. Carl Zeiss's London house, had stated that the objective 

 referred to by Mr. Merlin was not constructed to a new formula, but 

 was a picked one of the old series." 



Now, what is one to understand from all this ? For here is the 

 position : that Mr. Nelson makes the statement that he has ex- 

 amined hundreds of objectives upon this particular slide, and 

 presumably passed an opinion, which may have been adverse, upon 

 them ; hence the eulogy of this particular " new " lens in its mark- 

 ing of the step forward of the apochromatic, by reason of its power 

 to pierce the mysteries of the old balsam mount when all its rivals 

 had failed. If so, what is the actual scientific and commercial value 

 of this test ? In any case, before full acceptance, it would have to 

 overcome the controversial point of its being a marked instance of 

 the undue importance attached to a " pet slide " test, even though 

 in distinguished hands. 



Further, is Mr. Merlin the unfortunate possessor of a twelve- 

 year-old Zeiss \ apochromatic that has not " weathered " time and 

 constant use ? If so, his one-time second-to-none-in-existence 

 lens is verifying a prediction quoted by Mr. Nelson, as follows: 

 " That owing to the instability of these new fancy glasses there 

 would be a falling off in the performance of the finest kinds of 

 object-glasses." * Mr. Nelson, however, says that this has been 

 disproved over and over again, and is a fallacy only mentioned to 

 be destroyed forthwith by his own observations. But there is a 

 way out of the dilemma. To these questionings I can supply the 

 answer. The possessors of high-power apochromatics need not look 

 suspiciously upon their lenses, for all that are in use are by makers of 

 repute, and the plain fact is that if these tertiaries are present, in 

 a properly mounted specimen of mature valves of Concinodiscus 

 asterornphalus, they are resolved with comparative ease, and are 

 not so " extremely " elusive as to be only just within the grasp of 

 that lens, to quote Mr. Merlin's reference to his old Zeiss combina- 

 tion. And when present, now that their appearance has become 

 better known, they can be resolved and photographed by a 

 supposedly inferior lens. The photos (Series I., Z.), were taken by 

 me with an old Zeiss 2 mm. apochromatic, N.A. 1*30, projection 



* See this Journal, 1910, p. 147. 



