REVIEW

between the cable and the repeater station is in a situation peculiarly liable to great changes in insulation, necessitating a frequent adjustment of the artificial line in order to correspond to such variations. The advantage gained would, we doubt not, more than compensate for the slight increase in electrostatic capacity, due to the addition of a few miles of underground work.

The repeaters above referred to have, in England if nowhere else, been brought to a high standard of perfection for fast-speed working, and form a very important factor in the scheme. It ought, perhaps, to be observed here that a repeater is a set of apparatus inserted at about the middle of a long line. If the line be very long, the number of repeaters is increased accordingly. The currents arriving from the sending station pass through the coils of an exceedingly sensitive relay, and then go direct to earth. These currents impart to the relay tongue a motion precisely similar to that of the lever of the original sending apparatus, and the tongue is thus pressed against contact points connected to batteries, so that it sends forward to the receiving station currents which are precisely similar in character and duration to those sent by the forwarding station. The line is thus, to all intents and purposes, divided into two sections, each of about half the total length, and remembering that the factors which tend to reduce the speed of working vary as the square of the length of the line, the advantage will be apparent. Of course, a little loss occurs on account of the friction and inertia of the relay tongue and the inductance of the coils, but there is also the fact to be borne in mind that in the absence of the repeater it would be necessary to employ a battery of about double the electromotive force at the sending station, in order to produce currents of a given strength at the receiving office. It may be observed that the

toft; but in the case of a complete collapse the latter could, if necessary, be made a transmitting station, while, for ordinary interruptions, the underground lines would be invaluable for the repair of sections, as indicated presently. Coming south, the French cables present less difficulty. There is already a length of underground line about 14 miles in length carried to a point beyond Bromley; the addition of 56 miles or thereabouts would place London in underground communication with Beachy Head, where two six-wire cables land, and these could be worked as easily as at present by the insertion of repeaters at the Beachy Head repeater station. The shorter cables landing at Dover present even less difficulty, and repeaters at that station would render communication with the Hughes apparatus at present employed quite as easy through an underground line from London to Dover, as at present.

(To be continued.)

OPEN ENGINES IN THE NAVY.

OWING to the difficulties which have so frequently occurred with the closed type of engines formerly used almost exclusively in the navy for electric light machinery, the Admiralty have abolished them in their recent ships, and have substituted open engines of the compound type.

Our illustration shows one of a set of nine which Messrs. G. E. Belliss & Co., of Birmingham, have recently completed for the new battle ships. The firm have already supplied, during the last year or two (since the open type of engine has been adopted), about twenty of these sets of dynamo

"charge E.M.F. Under ordinary circumstances a single repeater suffices for our land lines. Thus, on a London-Aberdeen wire, the apparatus is inserted at Newcastle-on-Tyne, and at Preston on a London-Glasgow wire. Wires to the continent, however, frequently have two or more repeaters. On the LondonRome wire, for example, repeaters are inserted at Paris, Lyons, Turin, and Florence, so that the line is practically divided into five circuits.

imparted to the line varies directly as the

We shall have occasion in our next contribution to enlarge upon this question of repeaters; but, reverting to the subject of a systematic adoption of underground lines, we may say again that in all probability the lines which maintain communication between London and the continent would be among the earliest to receive attention; in fact, it will probably be remembered that after the big collapse of 1886 the demand for an underground reserve was almost as strong from Germany as at home. It is doubtful whether the longer of the German cables landing at Lowestoft could be worked with ease, as at present, if underground work were employed the whole of the distance from London to Lowes

machinery for various ships of our navy, and the official trials at Portsmouth have given complete satisfaction. The engine is well balanced, the cranks being opposite, and the valves arranged to give the amount of compression required for economy and quick running.

The makers have aimed at producing an engine capable of running for long periods without requiring adjustment, and with such simplicity of parts as shall render the liability to damage as small as possible and give the utmost facility for adjustment or repair. The cylinders are supported on four stout steel columns, fitted into long sockets, accurately bored to correspond in cylinder and bedplate. The guides are carried on the cylinder casting, and are designed to be very readily adjusted. The piston valves are placed at the back of the engine, and driven by a single lever arrangement from the H.P. connecting rod. The governor is placed at the end of the crank shaft, and is capable of controlling the engine to within 3 per cent. of the maximum revolutions when the full load is thrown suddenly off.

The engine and dynamo are carried upon a combination base-plate, and each set is subjected to thorough working tests at Messrs. Belliss & Co.'s works, where a very complete

FEBRUARY 6, 1891.]

installation of electrical resistances and recording instruments have been fitted for the purpose.

Each set supplied for service in our navy is also subjected to official tests at Portsmouth Dockyard for six hours' continuous running at full power, with a guaranteed minimum consumption of water per E.H.P. per hour, and the effectiveness of the governor and general perfectness of the whole construction and suitability for the service is determined. The illustration shows the engine in combination with a Siemens dynamo, but dynamos of other design and construction are fitted by Messrs. Belliss & Co. to their engines as may be required. We understand that they purpose to exhibit at the forthcoming Naval Exhibition some of their specialities in these things, and we have no doubt the simplicity and excellence of the design will attract the attention of all who are interested in this department of engineering.

HELLESEN'S PATENT DRY ELEMENTS.

THE want of an efficient dry battery has long been felt in both telegraphic and telephonic services, and, perhaps, even more especially for use in houses in connection with electric bells. After numerous unsatisfactory proposals, which failed to fulfil the requirements, greater success has been obtained during the last few years, and dry batteries which give general satisfaction are now coming into extensive use. It is evident that in cases where the liquids are subject to rapid evaporation, or where it is desirable to employ elements which, after their installation, require no further attention, and also in cases where portability is a condition to be fulfilled, dry elements will undoubtedly find their special field.

On the suggestion of Prof. Lommel, of the physical laboratory of the University of Munich, a series of experiments were conducted in November, 1889, by Mr. Heinrich Krehbiel, Dr. Narr and Dr. Donle, in order to obtain an exhaustive comparison of the electrical qualities of six of the principal dry elements in existence, viz., those of Hellesen, Bender, Thor, Gassner, Jenisch and Wolfschmidt.

A full report of these interesting experiments was published on the 1st of August, 1890, in No. 31, Vol. 11, of the Elektrotechnische Zeitschrift, of Berlin, containing a detailed account of the following investigations :

:

1. Change of the electromotive force of the element on open circuit.

2. Variation of electromotive force with temperature. 3. Determination of internal resistance.

4. Fall of electromotive force on a closed circuit, and subsequent recovery on open circuit, under the following conditions:

(a) With an external resistance of 3 ohms, furnishing a strong current ;

(b) With an external resistance of 50 ohms, furnishing a weak current.

As the complete report of the Munich University is a very lengthy document, we only extract from it the principal data referring to that element which proved the most satisfactory, viz., Hellesen's, and quote only such results with regard to the other elements as enable their respective efficiencies to be directly compared with that of Hellesen's cell.

The electromotive force was measured by an Edelmann's cylinder quadrant electrometer, by comparison with a Latimer

169

Clarke's standard cell of 1·407 V (the coefficient for reducing the electromotive force to the standard temperature being taken as 0.08 per degree Centigrade, as given by Helmholtz and Kittler).

The measurement of resistances was effected by Kohlrausch's method, using alternate currents, with the telephone introduced into the bridge. The Hellesen's cells had the following dimensions:-8 cm. square by 16 cm. high (3 inches square by 6 inches high).

The mean original electromotive force in volts at 15° C... taken immediately after the receipt of the cells, was 1.415 V. The electromotive force of each cell was tested periodically during 2 months, and remained with slight variations practically constant, no current, however, being taken from the cells during the time.

The electromotive force was at 0° = 1·405 V.; at 15° = 1-404 V.; and at 30° = 1·404 V.; showing that the electromotive force was practically unaffected by change of temperature.

The mean original internal resistance, taken immediately after the receipt of the cells, was 0.067 ohm; this resistance being lower than that of any of the other cells submitted for testing.

After these tests one element of each kind was continuously closed for 36 hours through an external resistance of 3 ohms and periodically tested; the results obtained with Hellesen's cell being the the following:

The experiments proved that all the elements increased somewhat in resistance, when short-circuited in this way for a long time.

The next and most important trials refer to the recuperative power possessed by these cells. For that purpose they were closed for 60 minutes through an external resistance of 50 ohms, after which time the circuit was opened and the amount of recovery observed at intervals. This closing and opening of the circuit was repeated 25 times, the circuit of each element being closed for 60 minutes at a time, and the elements then left on open circuit for 24 hours, thus imitating in some degree the demands required in actual work.

The following table shows the decrease of the electromotive force during the 60 minutes of closed circuit and the recovery during the 24 hours of open circuit given by the first of these 25 tests.

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A far more crucial test was then made by closing each element continuously for 96 hours through an external resistance of 50 ohms, after which time the circuit was opened for 24 hours, and the amount of recovery observed. The results are contained in the foregoing table.

According to the above table, the Hellesen element suffered the least loss in electromotive force after 96 hours' work on closed circuit, retaining 1-207 V., or 87.5 per cent. of its original value; but the table also shows that the Hellesen element possessed the greatest recuperative power, attaining after 24 hours' rest, 1.297 V. or 94.1 per cent. of the original value before the 96 hours of closed circuit.

After these experiments were brought to a close, a final test was taken by closing the cells for 60 minutes through an external resistance of 50 ohms, and then leaving them open for 24 hours. The following table gives the electromotive force in volts during this test :

[FEBRUARY 6, 1891.

In the foregoing experiments the circuit was closed through an external resistance of 50 ohms, but similar experiments were at the same time carried out through an external resistance of only 3 ohms. In these latter experiments the time of closed circuit was, however, only 30 minutes instead of 60 minutes; the number of periods being as before 25 respectively at intervals of 24 hours each.

The results obtained with Hellesen's cells after the first period of 30 minutes' work and 24 hours' rest are given in the following table, and it appears that the Hellesen's element suffers the least polarisation.

0.343

0.277

0.267

OPENED.

ninth, seventeenth and twenty-fifth period of 60 minutes, when the circuit was closed through an external resistance of 50 ohms.

The above table demonstrates the superiority of the Hellesen element, the value of the ampère-hours during the twenty-fifth period belng actually 96.7 per cent. of that furnished during the first period of closed circuit. This superiority is still more clearly shown by the ampère-hours which were furnished by the crucial test of the 96 hours on closed circuit, and which are as follows:

Thor

Gassner

Jenisch

Wolfschmidt

The ampère hours resulting from the final test and the

The next table gives the values of ampère hours at the first, ninth, seventeenth and twenty-fifth period when closed through an external resistance of 3 ohms. The duration of each period being 30 minutes.

This investigation of the comparative efficiency of the above elements was concluded by the experiment of regenerating the partially exhausted cells by a treatment similar to that of a secondary battery, i.e. by sending a current from two Bunsen elements during two hours through the cells. The elements thus regenerated were again worked for five periods of closed circuit (each period of 30 minutes, duration) through an external resistance of 3 ohms.

The following table shows the electromotive force of the partially exhausted Hellesen cell before and after its regeneration by the two Bunsen elements, and also the electromotive force of the last period of closed circuit, with the recovery after being on open circuit for 24 hours.

ELECTROMOTIVE FORCE IN VOLTS.

The Munich report contains the following conclusion as the results of this exhaustive and carefully conducted series of experiments :

"The most efficient elements, even for circuits of a small external resistance, are Hellesen's and Bender's elements. Hellesen's element excels Bender's by having somewhat less polarisation and much smaller internal resistance; it has, however, when exhausted by long working, not quite so much recuperative power as Bender's.

"A similar relationship exists between Thor's and Gassner's element. In a circuit with a small external resistance, Gassner's is less constant than Thor's, but the former has the advantage of more recuperative power, even after the electromotive force has been reduced to a very small value.

"Jenisch's and Wolfschmidt's elements are, in consequence of their very rapid polarisation, unsuitable for giving even approximately constant currents; hence they are only applicable when the duration of closed circuit is short. very

The above experiments prove that dry elements are well adapted for many practical purposes, especially for telegraphic, telephonic and similar services, and the considerable powers of recovery possessed by such elements gives them a long duration of life.

Hellesen's elements being able to produce strong currents during a long period, are well adapted to supersede the cells of Leclanche, Meidinger and similar types, and in many cases even those of the Daniell type.

Besides the electrical advantage shown in the tables accompanying the Munich report, there are various other advantages of a purely practical character possessed by such cells. when compared with wet elements.

The former are transported with far more facility, being always, and without any previous preparation, ready for use,

MR. CROOKES'S PRESIDENTIAL ADDRESS.

By S. ALFRED VARLEY ·

No. II.

THE passing reference to the molecular theory of gases made by me in my article on Mr. Crookes's address has led to certain comments and questions which it has seemed to me could be better dealt with in a communication than in the form of a letter. I am not sure that I clearly grasp the contention of my critic, but I think the spirit of it is, given constant pressure and constant temperature, that the gaseous molecules, on the assumption that they bombard one another, would simply give and take energy; in other words, that being perfectly elastic, no transformation of energy would result from the mutual bombardment of gaseous molecules.

I do not propose to argue the question, but proceed at once to try and express more clearly what was in my mind at the time I wrote the passage which has been criticised. Assume a pendulum under the influence of gravity, but suspended frictionlessly in absolute space, and there will be no power within the pendulum itself to set up motion; but if the bob be raised in opposition to the force of gravity, and then be set free, oscillations will be set going by the combined forces of the energy imparted to the pendulum bob and the action of gravity. Under such assumed conditions, the pendulum' would oscillate for ever, the amplitude of the oscillations being all of them equal; eliminate gravity, and bob of the pendulum will cease to oscillate, but the rod and point of suspension will be subject to stress proportionate to the energy imparted to the pendulum. It should not be overlooked that gravity was the fulcrum which enabled the pendulum bob to be lifted, and that although the raising of it has involved an expenditure-more correctly a transformation of energy-the act of lifting it has not imparted any energy to it; lifting the bob is simply altering its position in respect to the earth in such a way as to enable gravity to act upon it, the point of suspension of the pendulum now becomes the fulcrum which enables the force of gravity_to act upon the pendulum bob. I have dwelt on this matter because it seems to me not to be very clearly grasped, the idea often appearing to be that when you lift a weight, you impart energy to it. What really occurs is a transformation of energy in the person himself who lifts the weight, the equivalent of which is represented by the mass multiplied by the height to which it has been raised in opposition to the force of gravity. Increasing the distance between a mass of matter and the centre of the earth is suggestive of what takes place when, say, an india-rubber cord is extended

Now assume two gaseous molecules in absolute space propelled against one another by equal amounts of energy, the effect of striking one another would be to reverse the direction of motion, the molecules separating farther and farther from one another.

In the case of, say, our atmosphere, the gaseous molecules are under the influence of two forces, viz., energy and gravity; the former tends to push the molecules apart, and the latter pulls them towards the earth, and the consequence is that the molecules are under a condition of stress, impart additional energy to the gaseous molècules, and they become separated farther apart; increase the force of gravity, and the molecules are brought closer together. Now I am disposed to regard gaseous molecules as elastic springs, and that they do not possess the power of indefinite expansion, for the logical outcome of the present theory seems to me that our atmosphere should diffuse itself throughout space and leave the earth altogether; at the same time I confess I am sorry that I have involved myself in an argument on the molecular theory of gases, for arguments of such nature are at the best simply mental exercises which seldom lead to results of any practical value.

*In gaseous matter energy is combined with matter, but in the. case of matter in motion it is only associated with it.

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The present theory of matter is more or less connected with the agnostic theory of creation, and it seems in effect to be assumed that in some mysterious manner matter possesses the power to change its own properties; for example, our physicists admit that matter attracts matter, but at the same time they assume that molecules in the gaseous condition can set up a repulsive force when approaching one another, and the general outcome is that the atoms of matter and their associated forces are the only immortal entities in existence, and that they possess within themselves the power to create solar, stellar, and terrestrial systems, and it logically follows vital organisms also.

If I were asked to define theorists as contrasted with practical men, I should describe the best examples of both as possessing mental capacity in an equal degree, the chief difference between them being that the one thinks he knows and the other recognises the fact that he does not know. It is contended that those who are capable of realising how little they really do know are the more receptive to the teachings of our great Schoolmaster, Nature, and that being so, they, on the whole, make fewer mistakes. The following passage occurs in a published letter of Dr. Silvanus Thompson in the Electrician of the 23rd ult. :-"Only a halfeducated electrician would dream of applying a law that is true of steady currents to currents that are not steady;" but this is what the distinguished physicists who formed the British Association Unit Committee did do, until such time that Lord Rayleigh called attention to the errors which had been made, and I suppose Dr. Silvanus Thompson would hardly describe Sir William Thomson or the late Fleming Jenkin even, as half-educated electricians. Now, I myself became acquainted, in a very practical manner, in 1856, with the difference of behaviour of transient and steady currents by observing what followed as a consequence of a lightning discharge striking a telegraph wire and bursting up the apparatus. What then took place taught me the conditions which lightning protectors should be designed to fulfil. In 1859 I had to deal with inertia resistance in connection with telegraph circuits under another aspect, and my late brother, C. F. Varley, was well aware of the inertia opposed by all electric circuits, but more especially electro-magnetic circuits, and he turned it to account when designing his translating apparatus. In 1862 I observed that no two different samples of copper, although adjusted to an equal resistance, had precisely the same action on a galvanometer when a current divided itself through them. A few years later this fact was generally known and intelligently dealt with by manufacturers of differential galvanometers, nevertheless it was overlooked by our physicists.

The opportunities possessed by endowed scientific professors for making purely scientific advances are much greater than those possessed by a busy practical man, and they ought to lead the way, as Faraday did. That they do not do so arises, I believe, from the character of their education, which results in an almost entire devotion of their energies to mathematically investigating mental assumptions. Work of such description is for the most part simply a mental exercise; it may be of a very high order, but nevertheless (so far as real progress is concerned) of very little more practical value than clever chess-playing.

Exception has been taken to my speaking of the + pole of an induction coil. Of course it is generally known, although my critic, "N. S.," would not seem to be aware of the fact that when the secondary circuit of a Rhumkorff coil is closed through a path of great resistance, such as that opposed by high vacua and air spaces, that the discharges are in one direction only.

I have discussed this matter at considerable length in previous communications, for it is a subject I have gone into deeper than, I think, any of our physicists, as I hold that it forms the basis of the dynamo, and also of transformers. Whether the views I have published have been grasped by our physicists generally I cannot say, but one at least who writes much, talks glibly, and does not consider himself halfeducated, had the good taste to describe my views as absurd, when giving evidence in the Law Courts, but there is unfortunately abundant evidence forthcoming to demonstrate that our learned physicist's confidently expressed opinions, have not any real claims to be considered infallible.

Perform the following experiments :-Transmit rapidly one after the other a series of transient currents of short

[FEBRUARY 6, 1891.

duration through the primary wire of an induction coil, including a galvanometer in the circuit; when the circuit is open it will be observed that the energy unlocked in the galvanic battery and transmitted through the primary wire, as indicated by the galvanometer, is much less than when the secondary circuit is metallically closed; and that being so, it is evident that the closing of the secondary circuit, which, it may be remarked, is electrically insulated from the galvanic battery and the primary wire, has in some way or other reduced the resistance opposed to the passage of transient currents. The explanation which has been given in previous communications of this phenomenon is that when the secondary circuit is open, the passage of current through the primary wire involves magnetising the iron core; in other words, energy has to be occluded in the iron before current can pass, and this involves time; but when the secondary circuit is closed the energy, instead of being stored, seems to rebound, passing through the secondary circuit, where it becomes dissipated in the form of heat through the medium of current which it develops, and as the closed secondary circuit affords an outlet for the dissipation of energy, there is not nearly so much resistance opposed to the unlocking of energy in the galvanic battery.

The specific inertia resistance of copper is probably many hundreds of times less than that of iron; were it possible to obtain copper having no inertia resistance, then no magnetism whatever would be developed in the soft iron cores of transformers when rapid alternations are being sent through the primary circuit, assuming, of course, that the secondary circuit is closed metallically by a short conductor. All circuits, especially when in the form of solenoids, do, however, oppose inertia resistance, and in proportion as they do so relatively to the inertia resistance of the iron core, magnetism becomes developed in iron cores of induction coils and transformers.

If the terminals of the secondary circuit of a Rhumkorff coil be joined together by a wire, alternate currents will be developed in it when the battery circuit is closed and opened through the primary wire; but when an air space divides the two ends of the secondary circuit, inertia resistance is opposed in the primary one, checking to a considerable degree the unlocking of energy in the galvanic battery, as the occlusion of energy in the soft iron core occupies time. The magnetism developed in the iron is the equivalent of the energy occluded, and when the soft iron core has become magnetised sufficiently highly the armature is attracted and the circuit divided by the make and break. The energy occluded in the iron (in the shape of magnetism) now becomes rapidly dissipated through the medium of current developed in the secondary wire, the voltage of this current being determined by the amount of energy previously occluded in the iron core, the number of convolutions in the secondary wire, and the rapidity with which the iron becomes demagnetised by the discharge of the statically occluded energy. Now, as the number of convolutions in the secondary wire is very great, and the interval of time in which the demagnetisation is effected is very small, the voltage is raised high enough to create a path through an air space.

It has been already stated that when transitory currents are being transmitted through the primary wire of an induction coil, the secondary circuit being closed at the time, that the energy unlocked in the galvanic battery seems to rebound from the iron core through the secondary wire, instead of becoming statically occluded in the iron. We have here an illustration of the transmission of energy through space. Energy is unlocked chemically, developing current in the primary circuit, and energy is dissipated through the medium of current set up in the secondary circuit, such current being in the opposite direction to that of the primary one.

Those who are capable of looking at physics as one great whole, cannot fail to be struck with the resemblance of what has just been described to that of, say, an elastic ball propelled in what we may call a primary path, and which encountering an obstacle rebounds through a secondary one, where the greater percentage of the energy which set the ball in motion becomes dissipated.

In the case of the elastic ball, the vehicle of energy travels through both the primary and secondary paths, but in the case of an induction coil or a transformer, the vehicle of energy, viz., electricity, does not travel from one path to the other, and the fact that the electricity does not do so supports the contention of the writer put forward in previous