ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
255 
MICROSCOPY. 
a. Instruments, Accessories, &c.* 
(2) Eye-pieces and Objectives. 
Microscope Objectives, f — Prof. T. J. Burrill read before the Ame- 
rican Society of Microscopists the following paper: — “ I had the honour 
of presenting to this Society, at its last meeting, a paper embodying my 
experience and opinions concerning the Microscope. I now wish to 
offer the result of personal experience in the use of various objectives for 
microscopical work, especially along the lines followed as a teacher 
and investigator of biological science. The task thus set before me is 
more difficult than that of last year. Little niceties of difference count 
much more in an objective than in the construction of stage, or rack-and- 
pinion adjustment ; and though one may be sure that his preference is 
not founded upon fancy, yet he may find it hard to state in words 
upon just what special characteristics he bases his choice. In the 
paper of last year the names of makers are carefully excluded; this 
time it is impossible to get along without reference by name to the 
manufacturers of the instruments cited. I heartily wish it could be 
avoided and accomplish the purpose intended, for it is a source of 
embarrassment to myself, and is also liable to he seriously misin- 
terpreted. All- that can be said in justification of what follows, is 
that I am under obligations to no one, either directly or by implica- 
tion, except as necessitated by truth and fair dealing, and that matters 
of personal interest are thoroughly placed aside, it I am capable of so 
doing. The articles used are all owued by myself, or by the institution 
in whose service I am, with one somewhat conspicuous exception, and 
that was loaned to me, upon request, for the purposes of this paper. 
No comparison is made with such as I have not had abundant oppor- 
tunity to test, and, with the exception just mentioned, with none that 
have not been in use during some years of time. In the paper upon 
Stands, a note was made upon the fact that we are prone to like best 
that with which we become acquainted. In the case of objectives, 
however, there is less room for such preference, because the mere 
handling of one is practically that of others, including the position 
and movements of one’s body when at work. To be sure, in order 
to get the very best results with a high quality objective, one must 
patiently learn to use that particular instrument ; but this is another 
thing. The force of habit has little to do in this last case, while it is 
exceedingly strong in the method of moving the object uuder the lens, 
and in the manipulations generally of the stand. 
It should also be stated that my work has chiefly been upon un- 
coloured objects mounted in water, with or without the addition of 
carbolic acid or glycerin, and upon coloured objects in balsam ; the 
main exception is that of diatoms in balsam, and in this case as a test 
for the objective rather than work upon the objects for their own sake. 
* This subdivision contains (1) Stands; (2) Eye-pieces and Objectives; (3) Illu- 
minating and other Apparatus ; (4) Photomicrography ; (5) Microscopical Optics 
and Manipulation ; (6) Miscellaneous. t Microscope, xi. (1891) pp. 321-8. 
T 2 
