


204. THE NORTHERN MICROSCOPIST, 

<2 SEES hea ee ee 
aperture they make may not be clearly seen, they somehow get 
into the body of the animal and gradually devour all that is in it; 
and after cleaning it as thoroughly as ants will a small skeleton, 
leave it a hollow but perfect form, It is now open to the chapter 
of accidents, and it can be no matter for surprise that the minute 
eggs of aquatic creatures enter into it and hatch there. This can 
be easily illustrated. The Secretary of a local Microscopical 
Society has endeavoured to verify or substantiate some of the 
more marked cases presented by Dr. Bastian. But his method 
of examination is, of necessity, an interrupted one. He has 
frequently called my attention to curious cases of apparent ‘ trans- 
mutation,’ and I have before me now some of his drawings of these 
taken from nature. 
(Zo be continued.) 

THE RELATION OF APERTURE AND POWER IN THE 
MICROSCOPE. 
By PRoFEssor ABBE, Hon. F.R.M.S. 
A paper read before the Royal Microscopical Society, roth May, 1882. 
I.—GENERAL CONSIDERATIONS AS TO WIDE AND NARROW APERTURES, 
i ee question of the relative values of high and low apertures has been much 
obscured by the one-sidedness with which it has been treated. One party 
of microscopists—the ‘* wide-aperturists ”—having recognized that high aper- 
tures are capable of exhibiting minuter details than low apertures, conclude 
therefrom that all microscopical work must be done with very wide apertures, 
and that low-angled systems are worthless. Another party, relying upon the 
fact that there are many cases in which low or moderate apertures perform 
decidedly better than wide ones, generalize this experience and deny that there 
can be any essential benefit in very wide apertures, asserting that all observa- 
tions, with the possible exception of resolving diatom strize, can be done as well 
with low-angled objectives. The premises of both these views may be said to 
be true, but true under conditions only; and by disregarding these conditions 
both parties arrive at conclusions which are equally remote from a proper 
estimation of the requirements of scientific work with the Microscope. My view 
of the question * is based on the following considerations :— 
ea eee be) he 
* As some suggestion appears to hav. 

e been made when the above paper was read 
as to my views having undergone a change, I beg to remind my readers that the views 
above explained are those which I have professed since 1873—the date of my first 
paper on the subject. My advocacy of wide apertures for minute objects appears to 
have been interpreted as an advocacy of wide apertures for all purposes—a misappre- 
hension which I am at a loss to account for, as nothing I have ever said or written 
could justify any such a supposition. 
All the catalogues of Mr. Zeiss issued sin 
the objectives there specified (and st: 
and under my direction) include no 
moderate apertures.—E, A. 
ce 1872 give practical evidence of this, as 
ated to be constructed according to my principles 
low and medium powers, except with low or very 


