516 Meeting of the British Association. [ Oct., 
On Saturday, the 22nd, the papers read before this Section were, 
with scarcely an exception, mathematical, and defy condensation. 
On Monday several Reports of Committees and some meteor- 
ological papers were read. Professor Morren read a paper “On 
some Curious Reactions of Chloride of Silver when in presence of 
Chlorine.” Moist chloride of silver recently prepared when enclosed 
in a glass tube with an aqueous solution of chlorine, gradually 
becomes blackened when. exposed to light, silver being reduced 
and chlorine liberated. On the sealed tubes being placed in 
darkness, the liberated chlorine would re-combine with the silver, 
again forming white chloride of silver. This decomposition and re- 
composition might be effected indefinitely. 
The proceedings on the last day on which this Section sat 
were opened by a description of “A Galvanometer for the Detection 
of small Electric Currents,” by F. H. Varley, Esq. The author 
explained that the smaller the magnet used in a galvanometer, 
the greater would be the sensitiveness of the instrument. He 
employs two forms—both of which had been found to answer ex- 
ceedingly well. The first consists in suspending, with a single 
filament of silk, a magnet made of the finest steel wire that can 
be obtained, and rendering its motion apparent by viewing it 
through a rectangular prism by means of a microscope, in the 
eye-piece of which is placed a small graduated scale, photographed 
on glass. The magnet appears to be a black bar bisecting the field 
of view; and, as the finest wire obtainable for this purpose appears 
as thick as a scaffold-pole when sufficiently magnified, it is obvious 
that the slightest motion of the magnet must be rendered con- 
spicuous by the image moving to and fro over the graduated scale 
placed in the eye-piece. The second form is more sensitive than 
the first. A small magnet, made of flat steel, polished on one face, 
is suspended in the usual manner by a single filament of silk, and a 
small micro-photograph of a graduated scale is placed at such a 
distance from the reflecting surface that each of the photographed 
divisions shall equal two minutes of arc as nearly as possible. 
The image of the scale thus reflected is sent in a line with the optic 
axis of the microscope, and any deflection given to the magnet 
causes the photographed scale to appear to move across the field 
of view. ‘The reflecting surface moving doubles the apparent 
motion, giving the amount due to the angle of incidence, plus 
that of reflection. A movement of one graduated division being 
produced by one minute of deflection, if magnified 60 times by the 
microscope, will render a motion equal to one second of arc apparent. 
The Hon. J. W. Strutt then read a paper “On a Permanent 
Deflection of the Galvanometer-needle by a rapid Series of equal 
and opposite Induced Currents.” This paper contained a short 
