of Edinburgh, Session 1880-81. 119 
Analysis. 
I. 
II. 
Mean. 
Water, 
17*42 
— 
17-42 
Silica, 
56-46 
56-58 
56-52 
Alumina, . 
16-28 
16-40 
16-34 
Lime, 
8-12 
8-01 
8-06 
Magnesia, 
•12 
-16 
•14 
Soda, 
— 
1-76 
1-76 
100-24 
which, corresponds to the usual formula of stilbite. viz. : — 
A1 2 0 3 , 3Si0 2 + f^ a a 0 0 1 3Si0 2 + 6H 2 0 . 
3. On a Simple Form of Selenium Cell, and Experiments 
therewith. By Prof. James Blyth. 
The cell is constructed as follows : — 
Take a brass crop-comb of the kind usually worn by little girls. 
Cut off from it two equal parts, each about 4 inches long. From 
each part cut out each alternate tooth, and bend round each part 
in the form of a cylinder, soldering the ends together with hard 
solder. Take a glass tube about 4 inches long and having a 
diameter equal to the diameter of the cylinder. Place the brass 
cylinders upon the glass tube, with the teeth facing each other, 
and adjust them so that each tooth left takes the place of one 
which has been cut out, taking care that the teeth do not touch 
each other nor the solid parts of the cylinder. 
Now heat the cylinder in a Bunsen flame to a temperature sufficient 
to melt selenium — about 220° C — and mb a stick of selenium over 
the spaces between the teeth, so that each space gets filled with 
selenium, which will now be in an amorphous condition. To 
anneal it, place the whole in an air-bath at a temperature of about 
150° C for an hour or so, when the selenium will assume a metallic 
and crystalline appearance. Allow it to cool gradually, and then 
solder on two copper wires to the solid part of each brass cylinder 
to serve as electrodes. The cell is now ready for use. 
In order to show the action of light on the cell, I placed it over 
VOL. XI. 
Q 
