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POPULAR SCIENCE REVIEW. 
ventor terms it the “ conglomerate mixture ” battery. The electromotive 
force is also higher than in the older form. He has also recently added 
depolarizing plates, which can be renewed from time to time. They are- 
simply attached by indiarubber rings to the carbon. 
It appears from careful experiments that the electromotive force of this 
arrangement is 1*46 of a Daniell element, and the resistance when new ’718 
S.U. The electromotive force, however, diminishes rapidly when the external 
resistance is low, recovering quickly when the battery is at rest. 
Electro-Optic Observations on Various Liquids form the subject of a paper 
by Dr. John Kerr, of Glasgow, following up his important observations in 
1875 on a new relation between electricity and light. He then showed 
the possibility of inducing double refraction in glass, carbon disulphide, and 
several other dielectrics, by the application of electric force. He now fur- 
nishes notes of a later and more extended series of experiments on the same 
subject. The methods are substantially the same as before ; but the means 
of observation have been greatly improved by assistance from the Govern- 
ment Fund. He uses a new plate cell, made of a block of selected plate 
glass, three-quarters of an inch thick and 8 inches long. Two fine holes are 
drilled right through it ; one parallel, the other at right angles to its length, 
crossing in the centre, equidistant from the two faces of the plate. Two 
other holes are subsequently made through the plate ; one a tunnel, 1 inch 
high and f inch wide ; the second, a slightly tapering hole, into which is 
fitted a glass stopcock, so as to open and close the vertical boring. The 
electric terminals within the tunnel are two balls of brass, a quarter of an 
inch in diameter. To these two brass rods pass from the ends of the block, 
being made water-tight at the outer ends by india-rubber washers. The 
brass balls are strongly electro-plated with silver, and turned in the lathe so 
as to present flattened spheroidal surfaces to each other, distant by one 
eighth of an inch from one another. The cell is closed at either end by panes 
of plate glass, ^ inch thick and 2 inches square, with interposed sheets of 
india-rubber. The whole is supported by glass pillars, terminating in a solid 
wooden stand. All is then covered by a thick coat of shellac varnish. 
The cell thus constructed is filled with the fluid to be examined by means 
of a small funnel drawn to a fine end. 
It is often necessary to introduce definite and very faint birefringent 
actions between polarizer and analyzer. For this purpose, slips are cut out 
of plate glass, inch thick, f inch wide, and 7 inches long. When such a 
strip is forcibly extended by means of a weight, it acts on the transmitted 
light as does a positive uniaxial crystal, with its axis along the line of ten- 
sion ; when compressed, as a negative of similar power and position. These 
are termed optical compensators, some of which are fixed and constantly 
stretched by weights below sixteen pounds ; others are held in the hand,, 
with their long axes inclined 45° to the plane of polarization. 
The various pieces are arranged as follows : — The ray is horizontal, fur- 
nished by a flat paraffin flame placed edgeways, passing first through a 
polarizing Nicol’s prism; then through the cell above described, the two 
terminals being connected, one with the prime conductor of an electrical 
machine, the other to earth. Then follow two compensating plates of glass, 
mounted vertically, so as to admit of the attachment of stretching weights 
