PROCEEDINGS OF THE SOCIETY. 
141 
their bodies made removable, so that the objective could be used as a 
simple Microscope. 
The arm carrying the body and the objective was made so that it 
could rotate on a pivot, and further it was often fitted with rackwork 
extension, so that it could traverse the stage in any direction. This 
feature of swinging the body to one side had however long disappeared 
from the Continental Microscope. Messrs. Powell & Leal and were the 
only makers to retain it. In this they did not plagiarize the Strauss- 
Durckheim model, but they preserved the continuity of an English idea, 
which at that time had become the common property of Microscope- 
makers, both here and in France. 
(3) A Microscope with an inner tube for an erecting lens was made 
by James Smith in 1826. 
With regard to this point Mr. Nelson said that, apart from absolute 
certainty of the fact, he thought that the erecting Microscope was about 
230 years old, having been invented by Eustachio Divini.* 
Dr. W. H. Dallinger said it was pointed out during the discussion f 
upon the paper, that so far from having remained the same, the Conti- 
nental Microscope had been perpetually changing until at length it had 
actually put on a mechanical stage. 
Mr. Nelson said it had not only been changing, but it had been pro- 
gressing towards the English model all the time. 
Mr. J. W. Gifford read his paper “ On a new Monochromatic Light 
Screen,” illustrating his subject by the exhibition of a number of photo- 
graphs of spectra of the colouring matters used, and also by the various 
colour screens which were shown by means of the lime light lantern. 
Mr. Nelson said he had listened with great inteaest to Mr. Gifford’s 
communication and regarded the work done as being most valuable and 
just what had been wanted for a long time. His investigations had 
solved some very important questions and the results attained would be 
of use not only for ordinary microscopical work, but also for photographic 
purposes. A new feature was getting a solution so strong that a suf- 
ficient depth of colour was obtained by the quantity which could be 
put between two cover-glasses. 
The President was sure that the Fellows of the Society would join 
in a hearty vote of thanks to Mr. Gifford for the account which he had 
given them of this very excellent piece of work in a direction where 
perhaps as much still remained to be done as in any other. The thanks 
of the meeting were unanimously voted to Mr. Gifford. 
Mr. T. F. Smith read the following paper “ On the Ultimate Struc- 
ture of the Valve of Pleurosigma Angulatum ,” illustrating his remarks 
by numerous photographs shown through the lantern on the screen : — 
“ It is now four years ago that I had the pleasure of reading before 
you a paper J on the ultimate structure of the Pleurosigma valve ; in 
which I claimed to have figured, for the first time, structure which up 
to then had only been guessed at by prior observers. My remarks then 
* See this Journal, 1887, p. 149, fig. 16. f See this Journal, 1893, p. 577. 
X See this Journal, 1889, p. 812. 
