230 THE NORTHERN MICROSCOPIST. 

pite the opinions of experts who know how to take all matters into 
consideration, and we would therefore advise the advocates of the 
superiority of third class objectives to waive their objections to better 
ones, until they are able to maintain their position both practically 
and theoretically. 
We would like to see every research annotated with the exact 
focal length and aperture of each objective employed; the length 
of tube and the quality of the eyepieces, factors too often left 
entirely out of consideration. 
It has been thought necessary to state the foregoing as we have 
lately heard it expressed as our view, that without a student is able 
to purchase the very widest aperture lens obtainable he had better 
refrain from becoming a microscopist. We are sorry to have been so 
completely misunderstood : a great deal of very useful work can be 
done, and, in fact, has been done, with lenses of very low air angle. 
What we principally object to is that third rate objectives, adver- 
“ised and sold as such, should be paraded before the microscopical 
tyro as being of equal quality with, if not even better than, the 
first class well corrected objectives of the same makers. 
Of course some of these remarks do not apply to Prof. Abbe’s 
paper ; the small aperture lenses which he there recommends are 
not those constructed with low prime cost as the principal object ; 
but good well-corrected objectives constructed on a formula cal- 
culated to yield a maximum amount of penetration with great 
working distance, 
This leads us to take into consideration Prof, Abbe’s paper, read 
before the members of the Royal Microscopical Society on March 
roth of the present year, and which may be found printed zz 
extenso on page 204 ef seg. of this Journal. We may say in this 
connection that this criticism has been forced upon us by the pub- 
lication of opinions not founded on facts, not demonstrated either 
diagrammatically or mathematically, but supported by general 
statements only, so that each reader of Prof. Abbe’s paper will deem 
it only reasonable that he should be allowed to interpret the 
inferences after his own fashion. 
Since this paper was written, and the photographs prepared, a 
second paper by Professor Abbe has appeared, and may be found 
in the August number of the Royal Microscopical Society’s Journal. 
With many points in the first paper we were in agreement; we have 
always used and advised to be used relatively low angles for small 
amplifications and wide apertures for high amplifications; but as 
our readers will plainly see the matter is one of degree, and it is 
only when we come to discuss how these amplifications with their 
various apertures shall be constructed and applied in practice, that 
we find ourselves so completely at variance with the views of Prof. 
Abbe, ' 


