240 PROCEEDINGS OF SOCIETIES. 
would not dare in the least to impugn the accuracy of Captain 
Hutton’s experiments) was due rather to a reddish tint assumed 
by the cell-walls than to the cell contents. Some protonematous 
growths have red and brown cell-walls, but, at the same time, 
distinctly green cell contents. 
Rev. Dr. Dickson exhibited some crystals, under the polari- 
scope, found by him in a liqueur called Trapistine, manufactured 
by the monks of the monastery “ Grace Dieu,’ near Besangon. 
The same crystals were obtained from a liqueur called “ Grande 
Chartreux,”’ manufactured by the monks of the convent bearing 
the same name not far from Grenoble. Although sugar is of 
course contained in considerable quantity, Dr. Dickson believed 
that there was another organic substance probably obtained from 
a plant. Dr. Dickson promised to pursue his examination of 
these crystals and to give additional information on another 
occasion. 
Mancuester Lirerary AND PHILOSOPHICAL SOCTETY. 
MICROSCOPICAL SECTION. 
First Ordinary Meeting, Session 1864-5. 
17th October, 1864. 
JosEPH SIDEBOTHAM, Esq@., President of the Section in the Chair. 
Mr. J. B. Dancer, F.R.A.S., read a paper “ On a Contrivance 
for regulating the amount of Light transmitted from the source of 
Dlumination to the Mirror of the Microscope.’ When viewing 
certain objects by transmitted light, and particularly with oblique 
illumination, a very slight alteration in the quantity and direc- 
tion of the light produces a marked difference in the appearance 
of the object, especially in Diatomacex, where a proper manage- 
ment of the light shows lines or markings invisible under ordi- 
nary direct illumination. The apparatus now exhibited is one 
easily made at a trifling cost, and consists of a circular dise of 
blackened tin or cardboard ten or twelve inches in diameter, with 
a number of perforations of various shapes and sizes—circular, 
cross-shaped, wedge-shaped, &c.—the centres of which are about 
3 inches from the centre on which the disc, placed perpendicu- 
larly, rotates. The form of perforations found generally most use- 
ful are parallel slits—slits at right angles to each other—wedge- 
shaped and circular openings. The objects under view must be 
well illuminated in the direction required, and then the disc, sup- 
ported by a pillar, is placed between the source of light and the 
