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.
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.
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.