i April 13. 1882] 
NATURE 
56r 
A current is sent along the wire a (Fig. 2) from the 
observatory. It traverses the coils, issuing by wire 4, 
and, during the first instant of time, takes its course along 
the conductor g, passing through iron wire and carbon, 
and by d, 7, back to the battery. The needle, however, is 
immediately deflected (in the direction shown by the 
arrow) pulling down the little lever ss, which, oscillating 
on the edge of a small vessel of mercury, and bearing a 
branch from the wire 4, completes a circuit of low resist- 
ance with the return wire 4, a branch from which commu- 
nicates with the mercury in the vessel. A current is now 
flowing free of the carbon. It may be balanced at D 
(Fig. 1), and the second operation commenced. This 
consists in switching the current by a commutator, so 
that it arrives by wire f, and returns by wire a. The 
current on arrival tends to restore the needle to the 
horizontal, pressing it against the stop P. This, also 
(being the best position for deflection), is designed to be 
its position of equilibrium; the counterpoise s, being 
utilised to this end. The needle being horizontal, the 
low-resistance circuit is open, and the current must pass 
through the carbon to return to the battery. It is then 
again balanced at D, and the resistance of the carbon 
accurately determined. 
Turning to Fig, 3 we find that the instrument used at 
D (Fig. 1) consists of a deep vessel of mercury aa, com- 
municating with a flexible reservoir A, which is under the 
control of the screws. A scale is mounted on the vessel 
carrying a marker, 7, which is movable on the screw 
attached to knob £; to the markera thread of carbon, 
similar to that in the distant barometer, is attached, it is 
kept vertical and rigid by a small varnished platinum 
weight 7, beneath the surface of the mercury. The 
marker is of ivory, and a binding screw, B, keeps the 
carbon in circuit, the circuit being completed through the 
mercury and iron wire L. 
For equalising the resistances in the bridge, when the 
barometer is out of circuit, the screw S is turned, and the 
mercury thus raised or lowered on the carbon, till the 
galvanoscope returns to zero. This being effected, and 
the barometer restored to circuit, the galvanoscope is 
once more brought to zero by turning the knob Kk. The 
marker M now reads the height of the distant barometer. 
The scale, in Fig. 3, may not really be one of inches 
and fractions of inches; it may have to be divided by 
experimentally comparing the two carbons. Probably it 
would be hopeless to expect them to be exactly similar in 
secticn throughout their entire lengths. 
There are many ways of rendering this method of 
determining the height of a barometer by resistance more 
sensitive. It was suggested to me, for example, to double 
the effect on the resistance of any movement, by replacing 
the iron wire in the barometer by a second carbon. With 
this arrangement, moreover, if we still retain but the one 
carbon for equalisation (Fig. 3), the range is doubled, and 
the chances of errors correspondingly diminished. 
Other meteorological instruments may also be read by 
this method. J. JoLy 
Pembroke Road, Dublin 
ELECTRICITY AT THE CRYSTAL PALACE 
1V.— Electrical Accumulators. 
HE new accumulator of Messrs. E. Volckmann and 
J. S. Sellon, exhibited at the Crystal Palace Elec- 
trical Exhibition, in connection with the Lane-Fox system 
of electric lighting in the Alhambra Courts, has already 
been announced, but its construction has hitherto been 
kept a secret for reasons of patent right. The storing- 
power of this new secondary battery may be gathered 
from the fact that 33 cells feed 201 Lane-Fox incan- 
descent lamps, nominally of 20-candle power for 7 hours 
at a time, if the battery is fully charged to start with. 
The actual light of each lamp, however, is nearer 30 
candles; and it is found that these lamps, which are 
designed to bear a 20-candle current from the generator, 
will stand a 30-candle current from the accumulator owing 
to its more uniform flow. 
Each cell is stated to contain 5 horse-power of energy 
acting for an hour, or 1 horse-power for 5 hours, and se 
on. It consists of a series of metal plates of some alloy, 
each plate being ;',” thick, and perforated with round 
4 inch holes, as close as they can be punched or cast. 
These plates are connected alternately in series like the 
plates of a condenser, as in the figure, and joined to two 
stout terminals, which are the poles of the cell. The 
holes are filled with a metallic paste, the composition of 
which is not yet divulged, but may readily be guessed, 
from the fact that metallic lead is reduced on the negative 
plates, and peroxide of lead on the positive plates. The 
spaces between the plates, which are placed nearly an 
inch apart, are filled up with water mixed with one-tenth 
part of sulphuric acid, to give good conduction. The 
whole is contained in a wooden trough about 30 inches 
square and 8 inches in thickness. The weight of each 
cell is about 375 lbs., including 295 lbs. of the metallic 
composition which isthe storing agent. The sparks 
given off on connecting several cells of the charged 
battery by a stout copper wire are remarkably violent, 
the deflagrated wire flying off in a perfect shower of red- 
hot sparks of copper accompanied by loud cracks. On 
examining the wire afterwards, it is found to be literally 
torn asunder in small pieces by the force of the discharge. 
A considerable quantity of hydrogen is evolved from the 
cells. 
The exhibition of Lane-Fox lamps fed from this battery 
is without doubt the most beautiful display of incan- 
descent lighting which has yet been made in this or any 
other country. This, however, is chiefly due to the 
designs of the ornamental lamps employed to show off 
the rich architecture of the Moorish courts. The arches 
of the courts are picked out with rows of lamps having 
bulb or opal glass, which give a very pleasing light, not 
in the least dazzling to the eye, but at the expense of 25 
or 30 per cent. of the light. A crystal chandelier of the 
same kind of bulbs hangs in the Lion Court, and itis a 
moot point whether these opal globes, or globes of clouded 
glass are not best adapted for incandescent lamps in 
dwelling-rooms and studies. It is certain that the naked 
lights, though absolutely steady, have a dazzling effect on 
the eyes if looked at, which cannot but be injurious to the 
sight. The gems of the display are, however, three 
Mauresque electroliers designed by Mr. E. R. Johnson 
for Messrs. Verity Brothers, Regent Street. These large 
pagoda-like lanterns are hung in the inner courts, and 
the lights contained inside are only visible through the 
