180 PHYSICS. 
always closed, an interruption taking place only when the extremity of the 
steel spring passes over one of the channels, which occurs precisely when 
the poles of the inductor have just been removed from the magnetic poles. 
There is, however, another connexion between g and fh, a brass spring 
being screwed into the left brass pillar, which presses against the middle 
division of h. The metallic conductors, 1 and R, which are to be held in 
the hand, are conductively connected, the one with the right-hand pillar, 
the other with the left. As often now as the galvanic current is interrupted, 
the shock passes through the body of the individual holding the conductors, 
and when the rotation is accelerated, the action of the shocks becomes 
almost insupportable. For producing powerful physiological effects, an 
inductor must be employed, consisting of a very thin wire wound a great 
many times about a reel of wood; if for other experiments a current 
of great quantity but of slight intensity be required, a few turns of very 
thick wire, wound immediately on the iron nucleus, will be sufficient. 
The former is called the intensity, the latter the quantity inductor. 
P1. 22, fig. 55, represents the magneto-electric machine of Clarke, differing 
from those of earlier construction in dispensing with mercury (as does also 
the machine of Ettingshausen). Here e is the magnetic battery, consisting 
of vertical horse-shoe magnets resting against four adjusting screws, which 
pass through the mahogany board, p. The battery is bound to the board by 
two strong brass bands which pass through apertures in it ; f is the intensity 
inductor, containing two coils of insulated wire (4500 feet long in Clarke’s 
creat machine) wound about the cylinders, g, g; the beginning of each coil 
is soldered to the inductor. An iron spring is seen at 2, which presses by 
one end against the hollow insulated cylinder, h, to which the ends of the 
coils are soldered. The other end of the spring is fixed in a brass plate 
fastened to the block a; k is a four-cornered pillar of brass, which fits in an 
aperture of a brass band on the left of the block of wood, c, and may be fixed 
in it at any required height. The brass strips on each side of the block ¢ 
must be connected by a copper wire. m is a metal spring, held in perfect 
metallic contact with k by the head screw. The remaining parts are intel- 
ligible of themselves from the explanation given of the last machine. To 
produce a shock,the two brass conductors, n and o, are taken in the hands, 
previously moistened with salt water; one of the connecting wires is then 
stuck in the hole of the brass strip to the left of c, the other in the hole at the 
end of the piece carrying the break /. On turning the multiplying wheel, d, 
which sets the conductor in motion, the individual having hold of n and o 
will experience a severe shock. r and s are a couple of directors with 
handles and a piece of sponge to assist in the medical application of the 
apparatus ; the sponge must be moistened with vinegar or salt water for the 
better conduction of electricity. 
Clarke made use of the apparatus represented in pl. 22, fig. 56, to decom- 
pose water, and to collect its elements in separate vessels. Here a’ is a 
«lass vessel in which are placed two glass tubes, 6’ and c’. To the right of 
these are seen two platinum plates immersed in the vessel a’ under the tubes. 
To these copper wires are soldered to connect them with c. The platinum 
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