1891.] NEW-YORK MICROSCOPICAL SOCIETY. 77 



kind of way" {Quekeit Club Journal^ July, 1890, pp. 124, 125). 

 I state Mr. Nelson's position without any purpose of discussing 

 it, and only to point out that it is this to which Mr. Smith 

 refers in his paper when he says: "This capacity of standing 

 more light was pointed out from the first by Mr. E. M. Nelson, 

 but has not received the attention it deserves, and the neglect 

 of this point has stultified the efforts of many microscopists, both 

 here (in England) and on the Continent, to get more out of ihe 

 new glasses than the old objectives." 



Mr. Smith's investigation of diatom-structure is thus closely 

 connected with Mr. Nelson's views and experiments upon the 

 diffraction theory Both will challenge the attention of practical 

 microscopists as well as physicists. I have not gone far enough 

 in my own investigations to warrant me in expressing a judgment 

 on the questions involved ; but I would urge every microscopist 

 to make his ordinary work the occasion for accumulating evi- 

 dence which may help settle the very important debate. My 

 suggestions are only such as are based upon the well-known 

 history of diatom-study and my own experience. They are 

 offered by way of clearing the field by pointing out the limits of 

 the discussion and the known facts which ought to be kept 

 firmly in mind in all such investigations. 



It is no reproach to the microscope as an instrument of inves- 

 tigation that there are limits to its powers and capabilities. Such 

 limitations are common to all methods of investigation. If, 

 trusting to my natural eyesight, I am trying to make out the 

 meaning of appearances on a distant hillside, I find at once that 

 all perception by the sense of sight is an interpretation of visual 

 phenomena which are not in themselves decisive. They may 

 lack clearness by reason of the mist in the air. They may be 

 obscured by something intervening, like foliage, or may be partly 

 hidden by inequalities of surface. .\ thousand things may pre- 

 vent clear and easy interpretation of what I see. I may have to 

 change ray point of view before I can reach a conclusion, or even 

 have to go to the object itself. If I cannot do this I may be left 

 in abiding doubt as to what I have seen. 



Microscopical examination is precisely analogous to this. If I 

 am examining a mounted object, I am tied to one point of view. 

 I cannot approach nearer, and cannot do more than note the 



