'^JmmSl, jiTy !ri^^^^^ PROCEEDINGS OF SOCIETIES. 57 
matter of convenience, and tlie articles must be considered as com- 
munications addressed to the Society. He (the President) hoped to 
invite discussion upon the subject at a future period. 
The President then proceeded to read a paper on " The Diatom 
Prism and the True Form of Diatom Markings." * 
Mr. Wenham said : Some time since he had determined the 
markings on some diatoms to be spherical, and that this discovery 
had not been made by any special mode of illumination, but by the 
examination of fractured specimens. In one of the fragments of 
Qmdratum a line of spherules had been detached like a row of beads. 
At the extreme end a single spherule had separated sufficiently to 
enable it to be examined in an isolated state. In another case a small 
piece of the scale had been broken out and laid over close to the 
opening, thus affording an immediate comparison of both sides of 
the scale at the same time, and clearly proving the appearance to be 
exactly similar on either. The diatoms in question are exceedingly 
brittle ; and if some of them are placed on a slide with water, and 
thin glass-cover pressed hard down, and the whole left till dry, on 
slightly moving the cover some of them will be broken, a portion 
of the fragments adhering to each glass surface in various forms of 
dissection. The President confirmed in a remarkable way the views 
which he (Mr. Wenham) had entertained. An item of great value in 
the mode of illumination used by the President was the length of the 
prism, which threw a line of light from the condenser ; and he thought 
that, by using a shorter prism of only one-fourth of the length, the 
same effect would not be produced. The relief in which the object 
was seen was very remarkable. In fact, it had all the appearance of 
a solid body illuminated from above. 
Mr. Browning said it was gratifying to know, that after having 
bestowed so much labour on the attempt to resolve the markings on 
diatoms, the President was able to exhibit the real facts by so simple 
a method. 
(The President explained that he had been able to use a power as 
low as the |- inch). 
Mr. Slack said it was very interesting to find that the deposition 
of silica in the living diatom takes place under purely physical laws ; 
and the appearances which had been described as occurring on the 
diatom-valves are exactly what can be produced in making artificial 
diatoms by Max-Schultze's process. The structure of the diatom- 
valve shows that the so-called "vital forces" do not trouble them- 
selves to interfere with the deposition of silica, according to chemical 
and physical laws. He had never seen the markings on diatoms so well 
and clearly shown as by the President's method, though he had long 
distrusted any mode of displaying them that did not lead to the same 
results. 
Mr. Joseph Beck said it would be in the recollection of the Fel- 
lows that his late brother made a photograph of a common tumbler, 
the surface of which was covered with hemispherical elevations ; and 
that the photograph was made for the purpose of showing that the 
hemispheres, under certain conditions, would present the appearance 
* This valuable communication is published in the present Number. — Ed, 
