1872.] Electricity. 535 
sition, that the leaves diverged with electricity of the same sign as the 
caoutchouc rod, any such judgment would be absolutely false. A + eleérified 
body would be taken fora —, and vice versa. Such error might be guarded 
against if, instead of bringing the caoutchouc rod near the ele&roscope, a 
small charge of —E were brought from the former, by means of a proof plane, 
to the knob of the latter, as the proof plane would not colle& sufficient elec- 
tricity to produce the disturbance observed in the other case.”’ 
Mr. Planté has recently described a new form of secondary battery. Two 
plates of lead (20 inches long by 8 inches wide), are rolled up in spiral, being 
separated from each other by a few strips of india-rubber. This spiral is 
placed in a jar containing acidulated water, and having a gutta-percha cover, 
on which are fitted bending screws connected with the plates. Twenty such 
elements are placed in two rows of ten each, and charged from the primary 
battery, which consist of two Bunsen’s couples. By means of a commutator 
of peculiar construction these secondary elements may be connected either 
for quantity or for intensity. When the elements are joined in series an 
electro-motive force equal to thirty Bunsens is obtained, giving a current by 
means of which platinum wire may be fused. In the secondary couples the 
chemical action generating the current is the reaction of hydrogen on peroxide 
of lead, the current from the primary battery having caused decomposition 
of the water oxidising one of the plates, and developing hydrogen on the 
surface of the other. By the above arrangement the quantity of electric 
work from the direct action of the primary is transformed by condensation. 
The case is somewhat similar to that of a hydraulic press or crane. Ina pile 
driver, i.e., a heavy body raised by degrees toa great height, by a series of 
successive efforts, is then left to itself, and gives back at once the greater 
part of the work thus expended on it. So, when, after charging, the secondary 
circuit is closed, the sum of the accumulated chemical actions caused by the 
primary current is given out in the form of a very intense current of short 
duration. The effect, when the couples are joined for quantity, corresponds 
to the fall of a very heavy mass raised a small height; when joined for in- 
tensity, to the fall of a small mass raised to a great height. 
Mr. W. H. Preece, of Southampton, gives the following information about 
lightning conductors :—Ordinary galvanised iron wire, known as No. 4, which 
is }-inch in diameter, tipped with a gilded brass point or cone, is amply 
sufficient for any dwelling-house. It costs about a penny per yard, and the 
brass cones would cost about sixpence each. Thirty shillings would pay for 
all the materials required for an ordinary house. The reasons for recommending 
this wire are these :—When telegraph poles were first erected in this country 
they were protected with lightning conductors. This practice was subsequently 
found to be too expensive, and was abandoned. Such “‘ earth-wires”’ or con- 
ductors, were, however, found to effect another and very important objea&, and 
their use was continued on all main lines. Mr. Preece says, I have never 
known a case of a pole so protected being damaged through a thunderstorm, 
whereas scarcely a thunderstorm occurs without some unprotected poles being 
injured. I remember, near Romsey, twenty unprotected poles being shattered 
by one discharge, and upon the Basingstoke and Andover line 15 per cent 
were found to have been struck. The line was renewed and earth-wired, and 
not a single case of damage has occurred since, though some years have 
elapsed. A pole was very recently found in South Wales with 8 inches of 
its top shattered—the earth-wire only went so far; the charge from that point 
went harmlessly to earth through the wire. The cross arms are frequently 
found damaged as far as the earth-wire, never beyond. Instances could be 
multipled ad infinitum, and as the wire used is generally No. 8 (170 inches in 
diameter), and sometimes even smaller, I think I am fully justified in saying 
that No. 4 wire, which is twice as thick, and offers half the resistance, is 
amply sufficient for the protection of our houses. The precautions necessary 
in fixing conductors are these :—(1) The conductor must be solid and con- 
tinuous from its gilded point to the ground; (2) Its conneétion with the ground 
must be sound and good. It may be connected with the iron, gas, or water 
