190 CORRESPONDENCE. 



cost him, as evidently they have, " immense labour." What is not so 

 easy to exj^lain is his not having discovered that what costs him so 

 much trouble, costs others neither trouble nor time. . And when they 

 are put forth month after month as " original researches," we can do 

 nothing but look on in silent wonder. 



Your obedient servant, 



S. Leslie Brakey.* 



A Proposal as to Diatoms. 



To the Editor of the ^Montlily Microscopical Journal.^ 



Dear Sir, — I think the thanks of all amateur microscopists who 

 are interested in making classified collections of diatoms are decidedly 

 due to Captain Lang, the President of the Reading Microscopical 

 Society, for his generosity in making public his method of selecting 

 and mounting diatoms, and for the very interesting paj)er on the 

 subject which appeared in the December number of your excellent 

 Journal. It is as a rider to his paper that I venture to trouble you 

 with these few lines, in the hope you will publish them, as I am of 

 opinion that if by a discussion of the subject some mode could be 

 discovered or agreed on by which amateurs might be able to purchase 

 prepared or unprepared diatomaceous material, or to interchange 

 small quantities — say even a single dip evaporated on a glass slide — 

 of gatherings containing dissimilar forms, great benefit would accrue 

 therefrom. I have had the pleasure of conversing and corresponding 

 with Caj^tain Lang on these points, and I know that his ideas and 

 mine on the matter are very similar ; therefore I have the less hesita- 

 tion in asking you to ventilate the subject. 



At jjresent, among amateurs, there exists much difficulty in 

 getting material which shall contain a great variety of species and 



equation, writing it in numbers instead of symbols we get at sight, without calcu- 

 lation, the value of q, and the required diameter is, at sight, one-fifth of it. Tliis 

 is the whole work. Not a cipher nor a letter has to be added. The reader can 

 now turn to p. 266, and, if he likes, improve himself in algebraic fractions, the 

 Binomial Theorem, and Infinite Series, by working through Dr. Pigott's " calcu- 

 lation." As for the equation itself, this and the method to be followed, and the 

 figure, everything except the wonderful workmanshij), are copied out of the 

 manuals, — a circumstance which Dr. Pigott did not think it necessary to 

 mention. 



* F.S. — Since this was written some prominence has been given in the last 

 Number to the instrument introduced, or revised, under the name of the 

 " Aplanatic Searcher." I ought, therefore, perhaps to add that none of the above 

 remarks have any reference to it : as its principle or construction has not formed 

 the subject of any one of the papers contributed by Dr. Pigott to this Journal. 

 Time and the sure test of experiment will determine its practical value ; mean- 

 time those outside a certain circle, knowing nothing, have of course nothing to 

 say. My criticisms apply only to the Mathematical Optics in this series of 

 papers, about the merit of which tliere has grown up, as it seems to me, so very 

 remarkable a misconception ; remarkable as showing the incredibly low level at 

 which the scientific knowledge of optics exists among P^nglish observers, when 

 many of tlieni — so skilful and accurate in observation as every part of this Journal 

 proves them to be — can yet believe these papers to be an accession to the stock of 

 our knowledge. — March 8th. 



