264 
PROCEEDINGS OF SOCIETIES. 
when fluid is introduced between the lens and cover not a feature 
in the principle of the reflex illuminator exists — all total reflexion 
has gone, and I should expect light to pass into the object-glass, and 
the field would no longer be a dark one. 
Yours truly, 
F. H. Wenham. 
P.S. — Fix a very thick piece of plate glass on stage of microscope 
with body set horizontally. The upper side of the plate is polished, 
the under side fine ground. Focus the top surface with an immersion 
ith or yV^h having the highest available aperture. Place a lamp at eye- 
piece end, and a disk of light will appear on the under ground surface. 
The diameter of this is the base of a cone, the apex of which is on the 
upper surface, and the angle of the cone is the diminished aperture of 
the object-glass — the angle that the extra immersion partisans will 
have it is increased by a water connection between the front lens and 
object surface. Therefore look sharply while an assistant introduces 
the water internaedium. According to their notion the disk should 
at once increase in diameter, but not the slightest change is visible ; 
all that the water has done is to straighten the sharp bend of the rays 
that before existed between the disunited surfaces. The angle in the 
plate of glass remains just as before. 
I need scarcely say that I am wearied with describing these simple 
demonstrations. They are quite in vain, because the spirit of much 
of the opposition has shown more of a desire to have the satisfaction 
or credit of stating me to be wrong than to aid in establishing a 
scientific truth. 
PEOCEEDINGS OF SOCIETIES. 
KOYAL MiCEOSCOPICAL SOCIETY. 
King's College, October 6, 1875. 
H. C. Sorby, Esq., F.E.S., President, in the chair. 
The minutes of the preceding meeting were read and confirmed. 
The subjoined list of donations to the Society was read, and the 
thanks of the meeting were voted to the donors. 
Mr. Slack drew attention to the turn-table which had been presented 
to the Society by Mr. Cox, and which was placed upon the table for 
the inspection of the Fellows. Also to a new form of microscope 
which had been kindly sent by Messrs. Beck for exhibition ; it had a 
strong and firm stand, and a set of powers up to a dry inch, and 
packed in a moderate-sized case which contained all that was really 
necessary for a complete student's course. Also to a new form of 
pocket lens by Mr. Browning, and which seemed to be a great 
improvement upon those generally in use ; it was an achromatic 
triplet, with an unusually large, flat field, and veiry fine definition. He 
