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1878. ] Microscopy. 703 
open to all persons interested in microscopical science, and with 
meetings to be held annually at places selected during the pre- 
vious meeting. After much discussion and no little difference of 
opinion as to radical points, the plan was adopted as a sr 
and Buffalo fixed upon as the place of meeting for next Augus 
The following officers were unanimously elected for the first year: 
President, Dr. R. H. Ward, of Troy; vice-Presidents, S. 
Dennis, of San Francisco, and . Vorce, of C Cleveland ; sec- 
retary, Dr. H. Jameson, of Indianapolis; treasurer, H. P. Atwood, 
of Chicago. The president-elect insisted upon declining election 
on the ground of having been presiding officer of the Congress, 
but finally withdrew his resignation. During the meeting papers 
were read on the following subjects, interesting discussions being 
drawn out by many of the papers : 
“Limit of accuracy attainable in measurements with the micro- 
scope,” by Prof. Wm. A. Rogers, of Cambridge. “Some new 
forms of mounting,” by Ce, Merriman, of Rochester. Abstracts 
of these two papers will be published i in a succeeding number. 
“Formule of objectives,” by W. H. Bulloch, of Chicago. The 
construction of several modern lenses of large immersion aper- 
ture was given in diagrams constructed from the lenses them- 
selves, with results remarkably close to those formerly obtained by 
tracing the light mathematically through the objectives according 
to the data furnished by the makers. 
“Angular aperture, 4 by Dr. G. E. Blackham, of Dunkirk, 
N. Y. This paper gave a full review of the literature of the sub- 
ject, limited angular aperture to the angular distance of the out- 
side rays of the widest pencil of light, which the object glass 
could gather up and bring to a focus, with the formation of a well 
defined i image of the object, and insisted upon the superiority, it 
all prp of well constructed objectives of extremely wi 
angle 
“ Angular aperture defined,” by Prof. Romyn Hitchcock, of 
New York. In order that the term angular aperture should 
recommended to the microscopists of the country as a convenient 
and uniform usage. The triangle method was proposed for gen- 
eral adoption, considering the angular aperture of a microscope 
objective to be the angle of the apex of a triangle having a base 
equal to the available diameter of the front lens, and a height 
equal to the actual focal length (working distance), measured in 
air for a dry lens, and in the fluid employed*for an immersion 
the collar being adjusted for the most perfect definition in every 
case. While nearly all the members seemed to be personally in 
favor of the usage proposed, a motion that the congress should 
attempt to settle the question by requesting its — ae oe : 
mea with so mo opposition that it was withdraw -o 
