269 



NOTES AND CORRESPONDENCE. 



The Nose-pieceTinder — My observations on the nose-piece 

 finder (inserted in your last number) have drawn me into 

 a little controversy with a scientific gentleman of great micro- 

 scopic experience.' 34 ' 



He says, (t I have just read your remarks on the applica- 

 tion of the double nose-piece as a ' finder/ It is, of course, 

 as good a one as we can have, provided the object is large 

 enough, or sufficiently opaque, to be seen by the H objective • 

 but when it is with great difficulty seen with the 1-inch, the 

 1 nose-piece, as a finder, is useless/ " &c. 



He then instances several of the smallest examples of 

 Diatomacese (e. g. Eunotia Bactriana) , which are so exceed- 

 ingly minute and (when prepared in balsam) so exquisitely 

 hyaline, that it is to be doubted if they can be discriminated 

 with so low a power as li-inch, &c. 



These objections have set me upon a very careful course of 

 examination and trial ; for nothing could be more unpleasant 

 to me than to find that I had misled any one by an erroneous 

 statement. But I am happy to say that the result has been 

 rather a corroboration of my former assertions, with only this 

 modification, that more ought to have been said on the 

 subject of eye-pieces; for a 1^-inch objective acting along 

 with eye-piece a is very different from the same with eye- 

 piece d, &c. Then, again, eyesights differ in quality ; some 

 individuals being able to see a smaller speck with a 2-inch 

 objective than others can with 1-inch, and so on. 



With 1 \ -inch objective and eye-piece a I can very dis- 

 tinctly see the spot in the centre of P. angulatum. With 

 eye-piece d an object not a fourth part that size might be 

 seen so as to be perfectly recognised. 



The same combination will also distinctly show the reticu- 

 lations on a scale of Morpho Menelaus. 



* Mr. F. Kitton, of Norwich. 



