2 ee ee EEE 
282 THE NORTHERN MICROSCOPIST. 


members upon the aperture subject, and when he is asked a single 
question on water and oil immersions has to declare, “I’m not well 
posted up in it—it is as well to admit a thing at once.” Comment is 
unnecessary. I enclosemyname, but notfor publication, if you please. 
And am, etc., 
MICRO, 

Mr. Shipperbottom, of Bolton, writes:—“ I have promised a paper 
on Photo-micrography and Micro-photography for the Bolton 
Society this session, and I am pushing forward the construction of 
a camera replete with several mechanical and optical fittings which 
experience has taught me to be useful in producing Micro- 
Stereograms as well as Mono-photographs. When completed I 
hope to give a practical demonstration before our Society, 
Your Shutter will be a most useful addition for the purpose of 
aiding in the production of that amount of penetration which is 
essential for the production of Micro-stereograms. I do not believe 
a presentable Stereo-photograph of the larger forms of Polycistina 
or Foraminifera could be produced without your shutter (or its 
equivalent, a smaller stop).” 

Mr. John Browning writes :—“I have read the discussion at the 
Manchester Microscopical Society on the aperture of objectives. I 
regret that my engagements will not permit me to write at any 
length on the theory of the subject, but I think a few lines on my 
practical experience may be interesting to some of your readers. It 
has been my custom for many years to test all my objectives before 
leaving the factory. This I have done with the usual well-known 
tests, and I have always, after using the ordinary A eyepiece, tried 
successfully B, C and D upon them. When the objectives have 
been so good as to satisfy me, I have found but little loss of defini- 
tion by using these higher power eyepieces. And here I would 
like to point out that the power of the eyepieces used in microscopes 
is very low as compared with the eyepieces used in Astronomical 
Telescopes. Of course, in this case, the image formed by the object 
glass of the telescope is magnified by the eyepiece in a manner 
exactly similar to the action of an eyepiece on the image produced 
by the objective of the microscope.” 

Dear Sir, 
May I crave your permission to make one or two remarks 
upon a paper recently read on the Aperture question before the 
Manchester Microscopical Society. The reader of that paper 
commenced by setting himself a task which he said was exceedingly 
easy, viz., to explain what is meant by “aperture.” Its easiness I 

