SOME RECENT APPLICATIONS OF ELECTRICITY--AN ELECTRIC PIPE LOCATOR
One of the great advantages of living in a town is the abundant supply
of gas and water. These necessary substances are conveyed to us along
underground pipes, and a large town has miles upon miles of such pipes,
extending in all directions and forming a most complex network. Gas
and water companies keep a record of these pipes, with the object of
finding any pipe quickly when the necessity arises; but in spite of
such records pipes are often lost, especially where the whole face of
the neighbourhood has changed since the pipes were laid. The finding
of a lost pipe by digging is a very troublesome process, and even when
the pipe is known to be close at hand, it is quite surprising how
many attempts are frequently necessary before it can be located, and
its course traced. As may be imagined, this is an expensive business,
and often it has been found cheaper to lay a new length of pipe than
to find the old one. There is now an electrical method by which
pipe locating is made comparatively simple, and unless it is very
exceptionally deep down, a pipe never need be abandoned on account of
difficulty in tracing it.
The mechanism of an electric pipe locator is not at all complicated,
consisting only of an induction coil with battery, and a telephone
receiver connected to a coil of a large number of turns of thin copper
wire. If a certain section of a pipe is lost, and has to be located,
operations are commenced from some fitting known to be connected with
it, and from some other fitting which may or may not be connected with
the pipe, but which is believed to be so connected. The induction coil
is set working, and its secondary terminals are connected one to each
of these fittings. If the second fitting is connected with the pipe,
then the whole length of the pipe between these two points is traversed
by the high-frequency current. The searcher, wearing the head telephone
receiver, with the coil hanging down from it so as to be close to the
ground, walks to and fro over the ground beneath which the pipe must
lie. When he approaches the pipe the current passing through the latter
induces a similar current in the suspended coil, and this produces
a sort of buzzing or humming sound in the telephone. The nearer he
approaches to the pipe the louder is the humming, and it reaches its
maximum when he is standing directly over the pipe. In this way the
whole course of the pipe can be traced without any digging, even when
the pipe is 15 or 20 feet down. The absence of any sounds in the
receiver indicates that the second fitting is not on the required pipe
line, and other fittings have to be tried until one on this line is
found.
AN ELECTRIC ICEBERG DETECTOR
Amongst the many dangers to which ships crossing the Atlantic are
exposed is that of collision with icebergs. These are large masses of
ice which have become detached from the mighty ice-fields of the north,
and which travel slowly and majestically southwards, growing smaller
and smaller as they pass into warmer seas. Icebergs give no warning
of their coming, and in foggy weather, which is very prevalent in the
regions where they are encountered, they are extremely difficult to
see until they are at dangerously close quarters.
Attempts have been made to detect the proximity of icebergs by noting
the variations in the temperature of the water. We naturally should
expect the temperature of the water to become lower as we approach a
large berg, and this is usually the case. On the other hand, it has
been found that in many instances the temperature near an iceberg is
quite as high as, and sometimes higher than the average temperature of
the ocean. For this reason the temperature test, taken by itself, is
not at all reliable. A much more certain test is that of the salinity
or saltness of the water. Icebergs are formed from fresh water, and
as they gradually melt during their southward journey the fresh water
mixes with the sea water. Consequently the water around an iceberg is
less salt than the water of the open ocean. The saltness of water may
be determined by taking its specific gravity, or by various chemical
processes; but while these tests are quite satisfactory when performed
under laboratory conditions, they cannot be carried out at sea with
any approach to accuracy. There is however an electrical test which
can be applied accurately and continuously. The electrical conducting
power of water varies greatly with the proportion of salt present. If
the conductivity of normal Atlantic water be taken as 1000, then the
conductivity of Thames water is 8, and that of distilled water about
1/22. The difference in conductivity between normal ocean water and
water in the vicinity of an iceberg is therefore very great.
[Illustration:
_By permission of_] [_Dr. Myer Coplans._
FIG. 43.--Diagram of Heat-compensated Salinometer.]
The apparatus for detecting differences in salinity by measuring the
conductivity of the water is called a “salinometer,” and its most
perfect form, known as the heat-compensated conductivity salinometer,
is due to Dr. Myer Coplans. Fig. 43 shows a diagram of this interesting
piece of apparatus, which is most ingeniously devised. Two insulated
electrodes of copper, with platinum points, are suspended in a U-tube
through which the sea water passes continuously, as indicated in
the diagram. A steady current is passed through the column of water
between the two platinum points, and the conductivity of this column
is measured continuously by very accurate instruments. Variations in
the conductivity, indicating corresponding variations in the saltness
of the water, are thus shown immediately; but before these indications
can be relied upon the instrument must be compensated for temperature,
because the conductivity of the water increases with a rise, and
decreases with a fall in temperature. This compensation is effected by
the compound bars of brass and steel shown in the vessel at the right
of the figure. These bars are connected with the wheel and disc from
which the electrodes are suspended. When the temperature of the water
rises, the bars contract, and exert a pull upon the wheel and disc, so
that the electrodes are raised slightly in the U-tube. This increases
the length of the column of water between the platinum points, and so
increases the resistance, or, what amounts to the same thing, lowers
the conductivity, in exact proportion to the rise in temperature.
Similarly, a fall in temperature lowers the electrodes, and decreases
the resistance by shortening the column of water. In this way the
conductivity of the water remains constant so far as temperature is
concerned, and it varies only with the saltness of the water. Under
ordinary conditions a considerable decrease in the salinity of the
water indicates the existence of ice in the near neighbourhood, but the
geographical position of the ship has to be taken into account. Rivers
such as the St. Lawrence pour vast quantities of fresh water into the
ocean, and the resulting decrease in the saltness of the water within a
considerable radius of the mouth of the river must be allowed for.
A “FLYING TRAIN”
Considerable interest was aroused last year by a model of a railway
working upon a very remarkable system. This was the invention of
Mr. Emile Bachelet, and the model was brought to London from the
United States. The main principle upon which the system is based is
interesting. About 1884, Professor Elihu Thompson, a famous American
scientist, made the discovery that a plate of copper could be attracted
or repelled by an electro-magnet. The effects took place at the moment
when the magnetism was varied by suddenly switching the current on or
off; the copper being repelled when the current was switched on, and
attracted when it was switched off. Copper is a non-magnetic substance,
and the attraction and repulsion are not ordinary magnetic effects,
but are due to currents induced in the copper plate at the instant
of producing or destroying the magnetism. The plate is attracted or
repelled according to whether these induced currents flow in the same
direction as, or in the opposite direction to, the current in the
magnet coil. Brass and aluminium plates act in the same way as the
copper plate, and the effects are produced equally well by exciting
the magnet with alternating current, which, by changing its direction,
changes the magnetism also. Of the two effects, the repulsion is much
the stronger, especially if the variations in the magnetism take place
very rapidly; and if a powerful and rapidly alternating current is
used, the plate is repelled so strongly that it remains supported in
mid-air above the magnet.
This repulsive effect is utilized in the Bachelet system (Plate XV.).
There are no rails in the ordinary sense, and the track is made up
of a continuous series of electro-magnets. The car, which is shaped
something like a cigar, has a floor of aluminium, and contains an iron
cylinder, and it runs above the line of magnets. Along each side of
the track is a channel guide rail, and underneath the car at each end
are fixed two brushes with guide pieces, which run in the guide rails.
Above the car is a third guide rail, and two brushes with guide pieces
fixed on the top of the car, one at each end, run in this overhead
rail. These guide rails keep the car in position, and also act as
conductors for the current. The repulsive action of the electro-magnets
upon the aluminium floor raises the car clear of the track, and keeps
it suspended; and while remaining in this mid-air position it is
driven, or rather pulled forward, by powerful solenoids, which are
supplied with continuous current. We have referred previously to the
way in which a solenoid draws into it a core of iron. When the car
enters a solenoid, the latter exerts a pulling influence upon the iron
cylinder inside the car, and so the car is given a forward movement.
This is sufficient to carry it along to the next solenoid, which gives
it another pull, and so the car is drawn forward from one solenoid to
another to the end of the line. The model referred to has only a short
track of about 30 feet, with one solenoid at each end; but its working
shows that the pulling power of the solenoids is sufficient to propel
the car.
[Illustration: PLATE XV.
_Photo by_ _Record Press._
BACHELET “FLYING TRAIN” AND ITS INVENTOR.]
To avoid the necessity of keeping the whole of the electro-magnets
energized all the time, these are arranged in sections, which are
energized separately. By means of the lower set of brushes working
in the track guides, each of these sections has alternating current
supplied to it as the car approaches, and switched off from it when
the car has passed. The brushes working in the overhead guide supply
continuous current to each solenoid as the car enters it, and switch
off the current when the car has passed through. The speed at which the
model car travels is quite extraordinary, and the inventor believes
that in actual practice speeds of more than 300 miles an hour are
attainable on his system.