58 
The President's Address. 
Professor Smith to Mr. Lobb^ American opticians are stated 
to have improved the details of the instrument, and it will be 
interesting to see it in what the inventor may consider its 
most perfect form. 
Some time last year Mr. James Brooke and Dr. Beale 
spoke of the advantage of using a Kelner eye-piece as 
a condenser for the illumination of certain delicate trans- 
parent objects. Since then Mr. Webster introduced a 
condenser bearing his name. He employed an achromatic , 
combination of considerable curvature, with a bull's eye in 
front of it, and he also devised a novel form of stops in the 
diaphragm which he employed. This apparatus yields ap- 
proximately good results with objects of various depths from 
one inch upwards, and with those of small apertures it gives, 
when required, a dark ground illumination. Mr. Highley 
introduced a variation which seems to be an improvement in 
the optical part of this apparatus ; he employed an achromatic 
combination, of which the inner lens is a bulFs eye of very 
great curvature. This instrument is well spoken of by those 
who have tried it, and like that of Mr. Webster's, it is 
adapted to a considerable range of powers. With very diffi- 
cult and delicate objects it does not, however, quite satisfy 
the requirements of observers, and Mr. Highley is now engaged 
in devising a further modification, which he expects will offer 
a combination of advantages not yet presented by any single 
instrument. 
In the January number of ^ Popular Science Review,' at 
page 116, mention is made of Collins- Webster's condenser. 
It consists of a double concave lens cemented to a very deep 
convex lens, and capable of being fitted beneath the stage of 
any ordinary microscope. Of this I will only briefly remark 
that I learn that it performs well, and gives some results that 
have only hitherto been obtainable by using much more ex- 
pensive apparatus. 
A very ingenious diaphragm has been also introduced by 
Mr. Collins, by the use of which power is given to the 
observer to graduate the aperture of illumination with great 
accuracy, and without losing sight of the object; this is done 
by the use of a screw, withdrawn or driven by a milled head, 
causing a lozenge-shaped aperture to gradually open and 
close till it is reduced to a mere point. 
For very many subjects of research this diaphragm is a great 
improvement on any diaphragm furnished with a number of 
holes. 
Messrs. Powell and Lealand have introduced into their large- 
angled condenser a new stop, consisting of two slits at right 
