106 CORRESPONDENCE. 
tude of the shell,”—that it is no uncommon thing to find large valves 
with fine markings, and small valves with coarse markings. 
It should be understood that in quoting my friend Mr. Hendry, 
there is no wish to underrate the very necessary labours of Mr. Dal- 
linger : many observers were in doubt concerning the identity of 
certain diatoms, and these doubts, I suppose, he has dispelled ; more- 
over, there was much, both in matter and manner, to make his paper a 
welcome contribution to our Transactions. 
In agreeing with Mr. Dallinger that “the microscopist is more 
generally concerned with the characteristics of the silicious skeleton 
than with the morphology and development” of the diatom, he will 
perhaps pardon me for regretting the fact as a misfortune and a mis- 
take. I believe that most of us waste too much time in testing our 
tools, to the neglect of the useful work which even the worst of them 
would enable us to do; while there is a certain large class among us 
who really seem equal to nothing else but testing their instruments ; 
their highest ambition is bounded by the desire to exhibit dots and 
“beads” in competition with their neighbour. These gentlemen only 
can answer Mr. Kitton’s question, “ What is microscopical science ?” 
It is buying many objectives, measuring and comparing them, boasting 
of them, testing, re-testing, and yet again testing them, but never, by 
any chance, making an original observation with them. 
Yours obediently, 
Hewry Davis. 
THe Osiigue ILLuMrINaTor. 
To the Editor of the ‘ Monthly Microscopical Journal.’ 
Srr,—The oblique illuminator, which I proposed to name after 
my friend the Rev. J. Bramhall, was, I know, a new thing, so far as 
he is concerned. On discovering the effective performance of a 
reflector parallel to the slide, he at once wrote to me to ask my 
opinion of its value, and also to ask whether it was new. I made a 
rough trial, and found, with every disadvantage, it resolved strize with 
ease, that had formerly taken me some time to bring out; and as I 
was not aware that this method of illumination had previously been 
described, I wrote a short description of it for ‘Science-Gossip’ and 
this Journal, calling it the “ Bramhall Illuminator.” 
On June 30, 1876, I received a letter from the Secretary of the 
Microscopical Department of the Providence Franklin Society (Mr. 
John Peirce), in which he tells me that “Mr. Norman Mason, of Pro- 
vidence, R.1., accidentally discovered some time ago identically the 
same thing as you describe as ‘ Bramhall’s Oblique Illuminator.’ He 
was endeavouring to find a piece of plate glass of uniform thickness. 
He used pieces of broken mirrors, strewed wit? Lycopodium, for the 
purpose of focussing, and was astonished at the illumination. He 
afterwards made use of this illumination for diatoms, and found, as 
you state, that the distance of the mirror from the object made quite 
a difference. Yours respectfully, John Peirce.” 
