142 
The Presidenfs Address. 
very fine defining quality_, uninjured by an extraordinary 
amount of power in the eye-piece. 
Mr. Thomas Ross has also effected a considerable increase 
in the apertures of the lower powers^ having availed himself 
of the advantages to be obtained from the various qualities 
of glass which can now be procured, together with certain 
facts developed during his researches connected with the 
improved construction of lenses for photographic purposes. 
The aperture of the l|^-inch objective now extends to 20°, 
while the 3-inch, 2-inch, 1-inch, and |-inch have a corre- 
sponding increase, and all bear well the very severe test of an 
unusually powerful eye-piece, thus also affording to the 
microscopist an additional range in the choice of amount of 
amplification. 
Messrs. Smith and Beck have also extended the aperture 
of their l^-inch objectives from 14° to 20°. 
I have also had the pleasure of examining, with great care, 
two object-glasses of high power, constructed by a gentleman 
to whom microscopists are deeply indebted, who has not only 
favoured us with the result of important investigations 
relative to vegetable development and other subjects, but 
who has done more to stimulate the professional opticians to 
elevate the standard of excellence, as regards their manu- 
factures, than any other microscopical devotee, I allude to 
Mr. F. H. Wenham, whose absence from our gatherings, 
though only temporary, is a source of regret to many. Mr. 
Wenham' s mechanical skill and persevering industry, con- 
joined with an ardent zeal for the prosecution of science 
generally, have enabled him to compete successfully with 
our first makers ; and the two object-glasses in question are 
such as would be coveted by the most fastidious. The one 
is about equal to inch focus ; the other, according to my 
calculations, about -^q, though the artist himself calls it ; 
but be this as it may, with an aperture of only 150°, its per- 
formance is of the very highest order and beyond all praise. 
In both of these lenses, Mr. Wenham has adopted a 
variation upon the usual method of adjustment for thickness 
of glass covering to the object, which, in my opinion, 
deserves imitation by our professional opticians. The im- 
provement I mean consists in two points, viz., in causing the 
back combinations of the lens to be the moveable portion 
instead of the front as is usually constructed ; and secondly, 
in allowing the motion to be more rapid, the whole move- 
ment of which it is capable being effected by a quarter turn 
of the collar. Thus constructed, the requisite adjustment 
can be made with greatly increased facility, and, with the 
