Messrs. Thomson & Bottomley have recently invented a peculiar circuit
cutter based upon the use of a metal whose melting point is
exceedingly low. Recourse is had to this process for breaking the
current within as short a time as possible. In this new device the
ends of the conductors are soldered together with the metal in
question at one or several points of the circuit. The metal employed
is silver or copper of very great conductivity, seeing that the
increase of temperature in a conductor, due to a sudden increase of
the current, is inversely proportional to the product of the electric
resistance by the specific heat of the conductor; that these metals
are best adapted for giving constant and definite results; and that
the contacts are better than with lead or the other metals of low
melting point which are frequently employed in circuit cutters.
[Illustration: FIG. 1.]
Fig. 1 represents one form of the new device. Here, a is the copper or
silver wire, and _b_ is a soldering made with a very fusible metal and
securing a continuity of the circuit. Each extremity of the wire, _a_,
is connected with a heavy ring, _c_, of copper or other good
conducting metal. The hook, _d_, with which the upper ring, _c_, is in
contact, communicates metallically with one of the extremities of the
conductor at the place where the latter is interrupted for the
insertion of the circuit cutter. The hook, _e_, with which the lower
ring, _c_, is in contact, tends constantly to descend under the action
of a spiral spring, _f_, which is connected metallically with the
other extremity of the principal conductor. The hooks, _d_ and _e_,
are arranged approximately in the same vertical plane, and have a
slightly rounded upper and lower surface, designed to prevent the
rings, _c_, of the fusible wire, _a_, from escaping from the hooks. In
Fig. 1 the position of the arm, _e_, when there is no fusible wire in
circuit, is shown by dotted lines. When this arm occupies the position
shown by entire lines, it exerts a certain traction upon the
soldering, _b_, and separates the two halves of the wire, _a_, as soon
as the intensity of circulation exceeds its normal value. The mode of
putting the wire with fusible soldering into circuit is clearly shown
in the engraving.
[Illustration: FIG. 2.]
Fig. 2 shows a different mode of mounting the wire. The wire, _q_, is
soldered in the center, and is bent into the shape of a U, and kept in
place by the pieces, _r_ and _s_. In this way the two ends of it tend
constantly to separate from each other. Messrs. Thomson & Bottomley
likewise employ weights, simply, for submitting the wire to a constant
stress. The apparatus is inclosed in a box provided with a glass
cover.--_La Lumiere Electrique._
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