In tune

IN TUNE

1902

"It is desirable that the inductioncoil should be in tune or syntony with the electrical oscillations transmitted, the most appropriate number of turns and most appropriate thickness of wire varying with the length of wave transmitted".

World
of Wireless

In 1902 Marconi holds a lecture for the Society of Arts, he tells about "Syntonic Wireless Telegraphy". Marconi discribes that signals from two different transmitters interfere with eachother, those signals were difficult to distinguish. He discribes a technique he developed which he called "synthonic wireless telegraphy". He had improved this technique which he had allready had discribed in his patent, dated june 1 1898. This reads:

Below you will find the complete article.

SYNTONIC WIRELESS TELEGRAPHY.

The very rapid advances which have been made in the art of telegraphy through space continue to attract much attention to this fascinating subject. What was stated yesterday to be impossible has now become possible, and what we regard as almost insurmountable difficulties may be removed in the immediate future. It is my desire in this paper to give a description of progress made, with special reference to the results obtained by tuning or syntonizing the installations. So long as it was possible to work only two installations within what I may call their shere of influence, a very important limit to the practical utilisation of the system was imposed.

Fig. 130

Fig 131

Fig 136

With simple vertical wires, as shown in Fig. 130 and Fig. 131, connected directly to the coherer and spark gap at the receiver and transmitter, as used by myself before 1898, no really satisfactory tuning was possible. It was, however, possible to obtain a certain selection of signals if various stations in the vacinity used vertical wires differing very considerably in length. Thus two stations communicating over a distance of say five miles and using wires 100 feet long, would not interfere with the signals transmitted by the other two stations, say two miles from the first, which were using aerials only 20 feet long and communicating over a distance of about one mile. The new methods of connecting which I adopted in 1898-i.e. (see Fig. 136), connecting the receiving aerial directly to earth instead of to the coherer, and by the introduction of a proper form of oscillation transformer in conjunction with a condenser, so as to form a resonator tuned aerial wire - were important steps in the right direction. I realised a long time ago that one great difficulty in achieving the desired effect was caused by the action of the transmitting wire. A simple straight rod in which electrical oscillations are set up forms, as is well known, a very good radiator of electrical waves. If this was in the beginning an advantage, by allowing signals to be received with a small amount of energy over considerable distances, it proved later to be one of the chief obstacles in the way of obtaining good resonance in the receiver. Now, as Dr. Fleming points out so clearly in his Cantor lectures on "Electrical Oscillations and Electric Waves," delivered before this society in November and December of last year, there is in connection with this part of the subject one point of great interest. "Both theoretical and experimental research show that in the case of conductors of a certain form the electric oscillations die away with great repidity." In all what we call good radiators, electrical oscillations set up by the ordinary spark discharge method cease, or are damped out very rapidly, not necessarily by resistance, but by electrical radiation removing the energy in the form of electric waves. Many mechanical analogies can be quoted which will point out the necessity of designing a persistent oscillator, in order that syntony may become apparent in properly tuned resonators. Acoustics furnish us with numerous examples of this fact, such as the resonance effects produced by the well-known tuning-fork experiment. Other illustrations of this principle may be given e.g., if we have to set in motion a heavy pendulum by means of small thrusts or impulses, these must be timed to the period of oscillation of the pendulum, since otherwise its oscillations will not acquire any perceptible amplitude. An illustration of this fact occurred to me some time ago while I was watching the rising of great bells in an Italian cathedral. As most of you probably know, the bells in many churches in Italy, as elsewhere, are rung from the bottom of the tower by means of ropes attached to the bells. The largest bells weigh several tons, and it usually requires two men to work for perhaps two minutes on the ropes before the combined effect of their pulls is sufficient to get the bell to attain an amplitude large enough to cause the hammers to strike. I obeserved on the occasion to which I allude that it required for each bell a number of well-timed pulls on the ropes in order to get them to swing, the larger bells requiring impulses further apart-i.e., of a lower frequency - than the smaller ones. It is perfectly obvious that if the pulls on the ropes had been wrongly timed it would have been impossible, with the same amount of power, to ring the bells.

The same kind of effect happens in a very small fraction of a second (instead of several minutes) when we try to induce electrical oscillations in a good resonator. If the form of this resonator be such as to cause it to be a persistent vibrator-i.e., one in which the electrical oscillations are not rapidly damped by resistance or radiation of waves - then it is necessary for us to employ a number of properly timed electrical oscillations radiated from a persistent oscillator tuned to the period of the resonator we desire to affect. (Fig. 138 and 139)

Fig 138

fig 139

As I pointed out before, a transmitter consisting of a vertical conductor as shown in Fig. 130 is not very persistent oscillator. Its electrical capacity is comparatively so small and its capability of radiating waves so great, that the oscillations which take place in it must be considerably damped. In this case receivers or resonators of a considerably different period or pitch will respond and affected by it. From the results obtained it would seem as if the transmitter were sending out a great variety of electric waves, resembling therefore a source of white light, and that each resonator picks out and responds to its own particular wave length. This view, however is incorrect ; the fact that, given certain conditions, various resonators will respond, even if their period be different from the natural period of oscillation of a transmitter, is to be accounted for by the consideration that all the energy of the transmitter is radiated in only one or two swings, with the result that oscillations may be induced in resonators of different periods, while if the same amount of energy be distributed in a great number of individual feeble impulses, their combined effect can only be utilised or detected by a resonator tuned so as to respond to their particular frequency. The tuned resonator will not hen respond to the first two or three oscillations, but only to a longer succession of properly timed impulses, so that only after an accumulation of several swings the E.M.F. becomes sufficient to break down the insulation of the coherer and cause a signal to be recorded. Notwithstanding the disadvantages for obtaining electrical tuning attributed to the form of transmitter shown in Fig. 130, selection of messages is possible when using, say, two or three transmitters having wires of considerably different lengths, and the induction coil or oscillation transformers on the receivers wound with varying lengths of wire in their secondary circuits, in order to cause them to be in tune or resonance with the length of wave of the transmitted oscillations, as pointed out in my British patent, dated June 1, 1898. This reads: "It is desirable that the induction coil should be in tune or syntony with the electrical oscillations transmitted, the most appropriate number of turns and most appropriate thickness of wire varying with the length of the wave transmitted." At St. Catherine's Isle of Wight, we had a transmitting station having a vertical wire 45 meters, and at sea, 10 miles from our receiving station at Poole, a ship with transmitting wire of 27 meters. It is therefore obvious that the wavelength of the electric oscillations radiated from St. Catherine's differed considerably from that radiated from the ship. Now, if at the receiving station at Poole we connected to a vertical wire two receivers, one having an induction coil with secondary in tune with the length of the wave emitted by St. Catherine's and the other with that emitted by the 27-meter feed wire on the ship, if St Catherine's and the ship transmit simultaneously two different messages these will be picked up at Poole, and each message will be reproduced distinctly on this receiver. I pointed out in a patent specification dated December 19, 1899, that the best results are obtained when the length of the secondary of the induction coils is equal to the length of the vertical wire used at the transmitting station; therefore the length of the secondary of the receiving induction coils was made equal to that of the transmitting wire. These results, although in a way satisfactory, did not appear to my mind a complete solution of the problem. I found it impossible to obtain the two messages at the receiving station, if the two transmitting stations were placed at equal distances from it. The following considerations may perhaps explain this failure. If the 27-meter transmitting wire was placed at the same distance from Poole as the 45-meter one-i.e, 31 miles-the waves emitted by the 27-meter wire would be too weak when they reach Poole to affect the receiver. On the other hand, if the 45-meter transmitter was placed at 10 miles from the receiver, then the waves radiated by it would be so strong as to affect the receiver tuned to respond to the 27-meter transmitter, and blur the signals. It thus became apparent that some different form of less damped radiator was necessary, in order to obtain more practical and more useful results. I carried out a great number of experiments by adding to the radiating and receiving wires inductance coil, on a principle similar to that suggested by Lodge in his 1898 patent, but without obtaining any satisfactory results. The failure was probably due to the fact that the electrical capacity of the exposed conductors became too small in proportion to their inductance. I then tried various methods for increasing the capacity of the radiating system. The first and obvious mode of effecting this is by an augmentation in the size of the exposed conductor, of the circumstance that an increased surface means increased facility for radiating the energy during the first oscillations, and also because large plates or large exposed areas are impracticable on board ship, and are always difficult to suspend and maintain in good position during windy weather.

The way out of the difficulty was discovered by adopting the arrangement shown in Fig. 132. Here we have an ordinary vertical radiator placed near an earthed conductor, the effect of an adjacent conductor being obviously to increase the capacity of the electrical radiating wire without in any way increasing its radiative power; and, as I had expected, syntonic results were not difficult to obtain with such an arrangement. Mention of this method has been made by Captain Ferrie, one of the members of the French commission which was present at the tests carried out across the English Channel in 1899, in a paper on wireless telegraphy. See paper "Etat actuel et progres de la Telegraphie sans Fil," read before the Congres International d' Electricite, Paris, 1900. Satisfactory results were obtained, and I was encouraged to continue my researches in order to improve the system. Early in 1900 I obtained very good results with the arrangement shown in Fig.133. This arrangement is fully described in a British patent application applied for by myself on March 21, 1900. In it the radiating and resonating conductors take the form of a cylinder, the earthed conductors being placed inside. This form of radiating and receiving areas is much more efficient than the one I have previously described. One necessary condition of this system is that the inductance of the two conductors should be unequal, it being preferable that the large inductance should be joined to the non-earthed conductor. I presume that in order to radiate the necessary amount of energy it is essential that there should be a difference in energy it is essential that there should be a difference in phase of the oscillations in the two conductors, as otherwise their mutual effect would be to neutralise that of each other. In the first experiment mentioned by Capt. Ferrie, this was obtained by simply using an earthed conductor shorter than the radiating or resonating one. When I used an inductance between the spark gap or oscillation producer and the radiating conductor, I found it possible to cause the electrical period of oscillation of the receiving cylinder to that of one out of several transmitting stations, from which one alone it would receive signals. The results obtained by this system have been remarkable. By using cylinders of zinc only 7 meters high and 1.5 meters in diameter, good signals could easily be obtained between St. Catherine's, isle of Wight, and Poole (distance 31 miles), these signals not being interfered with or read by other wireless telegraph installations worked by my assistants or by the Admiralty in the immediate vicinity. The closely adjacent plates and large capacity of the receiver cause it to be resonator possessing a very decided period of this own- i.e., it becomes no longer apt to respond to frequencies which differ from its own particular period of electrical waves which are sometimes probably caused by atmospheric disturbances, and which occasionally prove troublesome during the summer. It seemed very remarkable to me during my first test that an arrangement similar to that shown in Fig. 133 should prove to be a good radiator, and should enable such a considerable distance to be achieved with cylinders of so moderate a height. It is probable that the great majority of the electrostatic liner of force must be also true that a certain number leave the outer part of the external cylinder, exactly as in the case of an ordinary radiator. The receiver is not shown in the sketch, but consists of similar cylinders to those used for transmitting the receiving induction coil or oscillation transformer, being placed where the spark gap is shown in Fig. 133. The capacity of the radiator due to the internal conductor is, however, comparatively so large that the energy set in motion by the spark discharge cannot all radiate in one or two oscillations, but forms a train of slowly damped oscillations, which is just what is required. A simple vertical wire, as shown in Fig.130, may be compared with a hollow sphere of tin metal, which when heated, would cool very rapidly, and the concentric cylinder system with a solid metal sphere, which would take a longer time to cool. Mr. W. G. Brown suggested, in a patent specification dated July 13, 1899, the use of two conductors of equal length joined to each side of the spark gap, but he did not describe the inductance in series between them and the spark gap, which, according to my experience, is absolutely necessary for long distance work. Another very successful syntonized transmitter and receiver system was the outcome of a series of experiments carried out with the discharge of Leyden jar circuits. Taking for granted that the chief difficulty with the old system, as shown in Fig. 130, lies in the fact, as already stated, that the oscillations are very dead beat, I tried by means of associating with the radiator wire a condenser circuit, which was known to be a persistent oscillator, to set up a series op persistent oscillations in the transmitting vertical wire.

An arrangement, as shown in Fig. 135, which consists of a circuit containing a condenser and spark gap, constitutes a very persistent oscillator. Prof. Lodge has shown us how, by placing it near another similar circuit, it is possible to demonstrate interesting effects of resonance by the experiment usually referred to as that of Lodge's syntonic jars. But as Lodge points out, "a closed circuit such as this is a feeble radiator and a feeble absorber, so that it is not adapted for action at any distance." I very much doubt if it would be possible to affect an ordinary receiver at even a few hundred yards. It is very interesting to notice how easy it is to cause the energy contained in the circuits of this arrangement to radiate into space. It is sufficient to place near one of its sides a straight metal rod or good electrical radiator; the only other condition necessary for long distance transmission is that the period of oscillation of the wire or rod should be equal to that of the nearly closed circuit. Stronger effects of radiation are obtained if the radiating conductor is partly bent around the circuit including the condenser (so as to resemble the circuits of a transformer). I first constructed an arrangement, as shown in Fig. 141, which consists of a Leyden jar of condenser circuit in which is included the primary of what may be called a Tesla coil, the secondary of which in connected to the earth of aerial conductor. The idea of using a Tesla coil to produce the oscillations is not new. It was tried by the Post Office officials when experimenting with my system in 1898, and also suggested in a patent specification by Dr. Lodge, dated May 10, 1897, and by Prof. Braun, in the specification of a patent dated January 26, 1899. My idea was to associate with this compound radiator a receiver tuned to the frequency of the oscillations set up in the vertical wire by the condenser circuit. My first trails were not successful, in consequence of the fact that I had no recognised the necessity of attempting to tune to the same period of oscillation (or octaves) the two electrical circuits of the transmitting arrangement (these circuits being the circuit consisting of the condenser and primary of the Tesla coil or transformer, and the aerial conductor and secondary of the transformer). Unless the condition is fulfilled, the different periods of the two conductors create oscillations of a different frequency and phase in each circuit, with the result that the effects obtained are feeble and unsatisfactory on a tuned receiver. The syntonized transmitter is shown in Fig. 134.The period of oscillation of the vertical conductor, A, can be increased by introducing turns, or decreased by diminishing their number, or by introducing a condenser E, in the primary circuit is constructed in such a manner as to render it possible to vary its electrical capacity.

The receiving station arrangements are shown in Figs. 136 and 137. Here we have a vertical conductor connected to earth through the primary J of a transformer, the secondary circuit J, of which is joined to the coherer or detector. In order to make the tuning more marked, I placed an adjustable condenser across the coherer in Fig. 136. Now, in order to obtain the best results, it is necessary that the free period of electrical oscillations of the vertical wire primary of transformer and earth connection should be in electrical resonance with the second circuit of the transformer, which includes the condenser. I stated that in order to make the tuning more marked I placed a condenser across the coherer. This condenser increases the capacity of the secondary resonating circuit of the transformer, and in the case of a large series of comparatively feeble, but properly timed, electrical oscillations being received, the effect of the same is summed up until the E.M.F. at the terminals of the coherer is sufficient to break down its insulation and cause a signal to be recorded. In order that the two systems, transmitter and receiver, should be in tune, it is necessary ( if we assume the resistance to be very small or negligible) that the product of the capacity and inductance in all four circuits should be equal. A more complete and detailed description of this system is given in a British granted to me, dated April 26, 1900. I have recently found that Prof. Braun has recognised the necessity of tuning the circuits of the transmitter and receiver when using a Tesla coil in order to obtain syntonic effects, but I am not aware that such a proposal was published prior to the description given in the above-mentioned patent. Although little difficulty has been encountered in measuring the capacity used in the various circuits, the measurement or calculation of the value of the inductance is not so easy. I have found it impracticable, by any of the methods with which I am acquainted, directly to measure the inductance of, say, two or three small turns of wire. As for calculating the inductance of the secondary of small transformers, the mutual effect of the vicinity of the other circuits and the effects due to mutual induction greatly complicate the problem. Experiments have confirmed the fact that the receiving induction coils having the secondary wound in one layer and at a certain distance, say, two millimeters (to cause the capacity to be so small) as to be negligible), have a time period approximately equal to that of a vertical conductor of equal length (see patent granted to G. Marconi, dated December 19, 1899). If, therefore we are using an induction coil having a secondary 40 meters long on the receiver, I should use a vertical wire 40 meters long at both transmitting and receiving stations. By so doing I have the two circuits at the receiving station in tune with each other, and I only have to adjust the capacity of the condenser at the transmitter, which can easily be done, either by means of a condenser having movable plates that can be slid, more or less, over each other, or by adding or removing Leyden jars. If we start with a very small capacity which we gradually increase, a value of the capacity will be reached which will cause signals to be recorded on the receiver. Supposing the receiving system to be within the sphere of action of the transmitter, then the signals will be strongest when the capacity of the condenser is of a certain value. If we still increase the capacity, the signals will gradually die away, while if we go on increasing the capacity, and at the same time add inductance to the Arial, to keep it in tune with the condenser jar circuit, we are still radiating waves, but these do not affect the receiver. If however, at the receiving station, we add inductance or capacity to the wire, A, Fig. 136, and also to the ends of the secondary J2, we find ourselves able to receive messages from the transmitter, although we are utilising waves of a different frequency.

Fig 135

Fig 141

Fig 134

Fig 136

Fig 137

Fig 143

Fig 142

It is easy to understand that if we have several receiving stations, each tuned to a different period of electrical vibration, and of which the corresponding inductance and capacity at the transmitting station are known, it will not be difficult to transmit to any one of them, without danger of the message being picked up by the other stations for which it is not intended. But, better than this, we can connect to the same vertical sending wire, through connections of different inductance, several differently tuned transmitters, and to the receiving vertical wire a number of corresponding receivers. Different messages can be sent by each transmitter connected to the same radiating wire simultaneously, and received equally simultaneously by the vertical wire connection to differently tuned receivers. A further improvement has been obtained by the combination of the two systems. In this case the cylinders are connected to the secondary d of the transmitting transformer, and the receiver to a properly tuned induction coil, and all circuits must be tuned to the same period as already described. (see Fig. 143.) The tuning of the receiver to respond to the period of the transmitter, as used in the old form of transmitter shown in Fig. 130, or in the new one shown in Fig. 134, has enabled results to be obtained over considerable distances with moderate heights. Signalling has been successfully carried out over a distance of 50 kilometers with a cylinder only 1,25 meters high, 40 inches in diameter. This has led to the possibility of constructing portable apparatus for army purposes, which should be of great service in the field. I have succeeded in constructing a complete installation on a steam motor car. On the roof of the car there in placed a cylinder which can be lowered when travelling, its height being only six or seven meters, and by this means communication has been easily carried out with a syntonized station over a distance of 31 miles. A 25-centimeter spark induction coil worked by accumulators and the accumulators can be recharged by a small dynamo worked by the car motor. I believe such an appliance might have been of use to the besieged garrisons in South Africa and China. A strip of wire netting laid on the ground is sufficient for earth connection, and by dragging it along communication can be established, even when the car is travelling. I have recently obtained as good results by not using any "connection" to earth, but only utilising in lieu of earth the electrical capacity of the boiler of the motor car. I also find that signals can be transmitted a considerable distance with the cylinder in a horizontal position. Last spring I recognised the desirability of carrying out tests between stations situated at much greater distances apart than had been attempted herefore. A station was established at the Lizard. Cornwall, and on the first attempt communication was effected with St. Catherine's Isle of Wight, over a distance of 186 miles, which I believe is the record distance over which signals have been sent through space without wires. It is interesting to observe that signals were obtained over this distance with the transmitting apparatus as shown in Fig. 130, or with the arrangement shown in Fig. 134, provided always that a suitable resonating induction coil was employed at the receiving station. The amount of energy used for signalling over this distance is not more than 150 watts, but experiments with a larger amount of energy will shortly be carried out. In the case of four parallel vertical wires, 1.50 meters apart, 48 meters long, or in a strip of wire netting of the same length. It is interesting to note that in order to communicate between my stations at Poole and St. Catherine's (distance 31 miles) with the same amount of energy and the same kind of aerial wire, this must be 20 meters high to obtain signals of about the same strength as those obtained between the 186-mile stations with the 48-meter aerials. This goes to confirm many other results previously obtained, which indicate that with a parity of other conditions the distance varies with the square of the height of the vertical conductors at the two stations. I have always found this law fulfilled, if the height of the conductors at the two stations is approximately equal, although an attempt has been made recently to throw doubt upon its correctness. In March, 1900, there were in use in the Royal Navy in South African waters five installations of my system. The Admiralty was apparently well satisfied with its working, since in May of last year they decided to extend its adoption to thirty-two more ships and land stations. The conditions of the contract were that each apparatus, before being accepted should be satisfactorily worked by naval signalmen between two ships anchored at Portsmouth and Portland, over a distance of 62 miles, a considerable portion of which i.e, 18 miles lies over land, with intervening hills; and the height of aerial wire was specified not to exceed on each ship 49 meters. The apparatus was delivered in a comparatively short time, no sets having been found unsatisfactory. The apparatus supplied to the Admiralty is so far all of the old pattern i.e, the non-syntonized system and I have been informed that messages have been transmitted and received by naval signalmen between ships more than 160 kilometres apart. It sometimes occurs that the unfamiliarity of the operators with the particular kind of apparatus used causes unsatisfactory results to be obtained, but I believe this trouble will soon disappear. I am glad to be able to state that arrangements are being made to install my new syntonic apparatus upon several of His Majesty's ships. I believe that in no other navy in the world is wireless telegraphy being worked regularly over such considerable distances. My system is also used for communication between the Borkum Riff and Borkum lightship, in Germany, where an ordinary commercial charge is made for messages received for ships, and it is employed further on the Nord-Deutscher Lloyd mail steamer "Kaiser Wilhelm der Grosse." According to an official report of the imperial postal authorities of Oldenburg, the total number of commercial wireless telegrams transmitted from and to the lightship between May 15 and the end of October amounted to 565, and these 518 came from ships at sea, while 47 were transmitted to ships . Of the 518 telegrams 35.7 per cent were addressed to the north German Lloyd, and 64.3 per cent to other shipping firms. The installations are worked by ordinary operators in a most satisfactory manner, and on one occasion assistance was obtained for a man who was taken suddenly ill on the Borkum Riff, and it was thus made possible to hand him over promptly for medical treatment on shore.

Fig 140

Before concluding, I wish to say a few words on a method proposed by Prof. Slaby, and with which I have also carried out some experiments. As transmitter, Slaby uses an arrangement as shown in Fig. 140, which consists of a vertical conductor, in which is interposed a condenser, K, and a spark gap, B. The top off the wire is not free, but is connected to earth through an inductance, C D, and a wire E. At the receiving station the arrangement shown in Fig. 144 in employed. It consists of a vertical conductor, D C, connected to earth at C, which should be the nodal point of the waves inducted in the wire, D c, where there is joined another wire, termed an extension wire, of equal length. In this case Slaby places an apparatus which he calls a "multiplicator," connected to the coherer between the end of the extension wire and the earth, or by another arrangement (Fig. 144), he uses a loop wire, F G H D C E, the multiplicator being placed between E and F, in series with the extension wire, J.

By means of this arrangement, Slaby, on the 22d of December of last year, showed the reception of two different messages sent from two transmitting stations situated at unequal distances from the receiving station to be possible, one station being at 4 kilometres and the other at 14; thus obtaining a result which may be considered similar to that obtained by me some months previously over longer distances. We are not told what was the amount of energy used for the transmission nor the height of the vertical conductor at the receiving station or at the transmitting station at the Aberspree Kablewurks. We are only told that the transmission wire was suspended between the chimney shafts.

Fig 144

Very little information is given as to the appliance which Dr. Slaby calls a multiplicator. G. Kapp, who is probably acquainted with the details of Slaby's work, commenting on this paper of his, calls the instrument in question "an especially wound induction coil (induction-spule), the function of which is the increase the E.M.F. of the oscillations at the ends of the coherer." Upon reading this for the fist time, I assumed that the multiplicator was an oscillation transformer performing the function of those described in my patent, dated June 1, 1898, and also described in my Royal Institution Lecture of February 2, 1901. As I subsequently, however, discovered, Prof, Slaby, referring to the multiplicator, states: "This apparatus in its most simple form consists of a wire coil of a determined shape and form of winding, which depends upon the length of the wave. . . . I might call this apparatus, unknown to my knowledge up to the present, a multiplicator. It is not to be confounded with a transformer, as it has no secondary winding." This statement appears to me very ambiguous, as I always have understood that what we call transformers need not have a distinct secondary winding. An appliance called an auto-transformer was used by the Westinghouse Company for regulating the E.M.F. supplied to house/lighting installations, which consisted in a single winding, a certain number of turns acting inductively on the adjacent ones. "Page really made the first experiment in auto-induction and showed that different parts of the same conductor might act primary and secondary circuits to each other, if in contiguity." I installed the apparatus described by Slaby at Niton, Isle of Wight, and at Poole using 35 meters high, but with the receiving wire earthed at C (Fig. 144) of the loop, I could receive nothing, although I tried various frequencies of oscillation. It is, however, probable that I might have received, had I been working over much shorter distances than 50 kilometres, as Slaby did in his demonstration, or had I used a greater height of wire. By using, however, my method of connection, i.e., introducing between the vertical wire and earth an oscillation transformer, having its circuits tuned to the frequency given by an ordinary vertical radiating conductor of length equal to the Slaby wire, A C, I succeeded by means of extremely sensitive coherers in obtaining communication. I then tried the following experiment. I took down the earth wire, E D, and the Inductance, D C, and used only the conductor, A C, insulated, with the condenser in circuit for transmitting. An enormous strengthening of the signals at the receiver was immediately obtained, which obviously means a greater ease of working, and the possibility of obtaining signals over greater distances. The reasons which demonstrate that closed circuit, such as is employed by Slaby, must be a poor radiator, are obvious to those who have studied and read the classical works published since the time of Hertz's experiments. Dr. Slaby, however, states that the inductance at the top of his loop confines the oscillations to the vertical part, A C. If this be the case, the frequency of these local oscillations cannot be equal to that of the whole circuit, A C D E, which it has been stated was so easy to circulate, if the translations of Slaby's paper I am relying on are correct. I believe that notwithstanding the inductance, C D, a considerable amount of energy must pass to earth through the earthed wire, which acts as a leak uselessly dissipating energy which should be radiated into space in the form of ether waves. If these conclusions are correct, I am not at all clear as to what necessity there if for employing the earthed conductor, E D, and the inductance. It is not necessary for obtaining syntonic effects from transmitting stations placed at equal distances from the receiver, as these can be obtained when using the primitive form of transmitter shown in Fig. 130, and Slaby has not yet described how to obtain different messages from transmitters situated at equal distances from the receivers, which is much more difficult in my experience, nor does it appear possible with the method he describes to transmit various messages at the same time from one sending wire, as can be done with the system I have just explained. The distance obtained with the closed transmitting arrangement must be comparatively small. As I have already stated, communication over a distance of 300 kilometres is now being maintained with my system, but I am not aware of anything approaching even 100 kilometres being achieved with the loop transmitter. It may be said that long distances of transmissions are not necessarily an advantage, but I notice that the navy wants long-distance apparatus supplied to it. I have also tried connectors similar to Slaby's extension wire in the receiver, but I find that the real sifting out of waves is done in the oscillation transformer, although sometimes it may be desirable to increase the period of oscillation of the aerial conductor by adding inductance to it, or at other times to decrease the period by placing a suitable condenser in series with it. I have come to the conclusion that the days of the non-tuned system are numbered. The ether about the English Channel has become, in consequence of great wireless activity, exceedingly lively, and non-tuned receiver keeps picking up messages or parts of messages from various sources which very often render unreadable the message one is trying to receive. I am glad to say, however, that I am now prepared with syntonic apparatus suitable for commercial purposes. And, as my final word on the general subject for the present, let me say that those who are responsible for the recent development of wireless telegraphy into a practical science, cannot fail to find great satisfaction in the reflection that, as already life has been saved that without this discovery would have been lost, so in the future, apart from it manifold commercial possibilities, valuable as these are, humanity is likely to have before very long to recognise in telegraphy through space without connecting wires the most potent safeguard that has yet been devised to reduce the perils of the world's sea-going population.

(Marconi on his recent trip to his country, received distinct tape-written messages from Poldhu, Cornwall, until he was over 1.500 miles from that point, and since that time has succeeded in signalling from Europe to his country.)

Ref. Experimental Science, G.M. Hopkins (1902).