232 Intelligence and Miscellaneous Articles. 
The selenium-actinometer consists of a cylinder of selenium pre- 
pared on Mr. Graham Bell’s plan. Thirty-eight disks of copper 
are isolated from each other by disks of mica of smaller radius ; 
the groove thus formed is filled with selenium by being rubbed with 
a rod of this substance. The cylinder being suitably heated, this 
selenium acquires a greyish aspect, and is ready for use. The even 
numbers of copper are united by conductors, and the odd numbers 
also by another set of conductors. By this arrangement not 
merely is the resistance of the selenium lessened, but we may still 
increase the delicacy of the apparatus by increasing the number of 
disks and that of the layers of selenium, while diminishing the 
resistance of the latter. 
The selenium cylinder is insulated by glass supports in the in- 
terior of a glass cylinder, which is exhausted so as to protect 1t from 
the disturbing influence of obscure heat. 
The whole is placed on a support high enough to avoid the effects 
of light reflected from adjacent objects. In placing the cylinder 
care is taken to do it so that its axis is parallel to the terrestrial 
axis. In this way the sun’s rays strike the selenium almost per- 
pendicularly at any hour of the day and always illuminate the same 
portion. By a slight motion in the plane of the meridian the 
cylinder could each day be brought into such a position that the 
rays are quite perpendicular. 
If, now, we pass a constant current through this apparatus and 
through a galvanometer, the copper will show by its various deflec- 
tions all the changes in the illumination of the selenium. 
In order to compare these variations we must first adopta scale : 
if we suppose the selenium in complete darkness, its resistance will 
be a maximum, and the deflection of the galvanometer the least. 
The greatest effect would be to annul the resistance of the selenium ; 
by withdrawing the latter from the circuit we should obtain a 
greater deflection, which we call 100 or the maximum light. Divi- 
ding the interval thus obtained into 100 equal parts, we shall have 
actinometrical degrees which are always comparable. 
In practice the battery to be used would be that of Clamond. 
During the determination of the 100 point and cf zero the external 
part of the pole would be kept at zero. By repeating the operation 
at different external temperatures, we should obtain a table for 
reducing the actinometrical degree obtained at a given temperature 
to what it should be if the external part of the pile were at zero.— 
Comptes Rendus, Feb. 2, 1885. 
ON THE SYNTHESIS OF TRIMETHYLAMINE AND PYRROL FROM 
COAL-GAS 5; AND ON THE OCCLUSION OF HYDROGEN BY ZINC 
DUST. BY GREVILLE WILLIAMS, F.R.S. 
In a paper on “The Action of some Heated Substances on the 
Organic Sulphides in Coal-Gas,” * I mention that on passing coal- 
* See ‘ Journal of Gas Lighting,’ vol. xli. pp. 913, 960. 
