1 68 



NA TURE 



[December 9, 1909 



RESEARCHES IN RADIO-TELEGRAPHY} 

 II. 



IN a previous discourse explanations were given of the 

 property of a closed or partly closed antenna of radia- 

 ting more in some directions than others, and the action of 

 Marconi's bent antenna was described. Two other inven- 

 tors, Messrs. Bellini and Tosi, have taken advantage of 

 this fact to construct 

 antennae of a very interest- 

 ing character. They erect 

 an antenna consisting of 

 two wires, each bent into 

 a triangular form, the top 

 ends nearly meeting, the 

 planes of these triangles 

 being at right angles to one 

 another, and both of Ihem 

 vertical. The nearly closed 

 antenna circuits are then 

 inductively coupled with a 

 condenser circuit, which is 

 capable of being swivelled 

 round in various directions. 

 If the said condenser 

 ^ circuit is placed in such a 



Fig. 13. position as to be coupled 



with one of the triangular 

 antennae it will cause the maximum radiation to take 

 place in the plane of that antenna, but none at all at 

 right angles to it. If it is coupled with the other 

 antenna it will cause radiation to take place to a maxi- 

 mum degree in the plane of that second antenna. If, 

 however, the oscillatory circuit is placed in an intermediate 

 position, so as to act inductively upon both the nearly 

 closed triangular antenna;, then it can be shown, both 

 mathematically and experimentally, that the radia- 

 tion of the combined system is a maximum in the 

 direction of the plane of the oscillatory circuit which 

 is coupled with the antenna. Hence, with such a 

 combined antenna, we have it in our power to create 

 radiation most strongly in one direction, although 

 not entirely suppressed in all other directions. By 

 combining together, however, a single vertical 

 antenna with two nearly closed circuit antennse at 

 right angles to one another, Messrs. Bellini and 

 Tosi have constructed a complex antenna which has 

 the property of producing radiation almost entirely 

 limited to one-half the circumjacent space (Fig. 

 13). It therefore corresponds to a certain extent in 

 effect to the optical apparatus of a lighthouse, with 

 catoptric or dioptric apparatus, which projects thi." 

 light from the lamp largely in one direction. It is 

 not yet possible to make with electric radiation of 

 long wave-length that which corresponds precisely 

 with a beam of light wholly concentrated along a 

 certain cone or cylinder, but it is possible, by the 

 use of a complex antenna as described, greatly to 

 limit the diffusion of the radiation. Since radiatinf; 

 and absorbing power go hand in hand, it is obvious 

 that such a directive antenna also enables the posi- 

 tion of a sending station to be located. Messrs. 

 Bellini and Tosi have accordingly applied their 

 methods in the construction of a radiogoniometer 

 and receiving antenna, by means of which they can 

 locale the direction of the sending station without 

 moving the antenna, but merely by turning round 

 a secondary circuit into a position in which the 

 maximum sound is heard in a telephone connected 

 with the receiver. By the kindness of Captain Tosi 

 I am able to exhibit to you their ingenious apparatus 

 (Fig. 14)- 



The space occupied by such closed antennse has 'k 

 hitherto prevented their employment on ships. There 

 is still, therefore, an opening for the invention of apparatus 

 capable of being used on board ship which will enable one 

 ship to locate, within narrow limits, the direction of 

 another ship sending signals to it, and therefore of ascer- 

 taining immediately the direction from which some call for 

 help is proceeding. 



1 From a discourse delivered at the Roy.-il Institution, on Friday, June 4 

 By Prof. J. A. Fleming, F. K.S. Contmued from p. 144. 



NO. 2093, VOL. 82] 



We must pass on to notice, in the next place, some 

 improvements in oscillation detectors and means of testing 

 them. As already explained, the aether waves sent out by 

 the transmitting antenna fall on the receiving antenna and 

 create in it, or some other circuit connected to it, very 

 feeble oscillations. These oscillations being very feeble, 

 alternating currents of high frequency cannot directly affect 

 either an ordinary telegraphic instrument or a telephone, 

 but we have to interpose a device of some kind called an 

 oscillation detector, which is affected by oscillations in 

 such a manner that it undergoes some change, which in 

 turn enables it to create, increase, or diminish a local 

 current produced by a local battery, and so affect a tele- 

 phone or telegraphic relay. One kind of change the oscil- 

 lations can produce in certain devices is a change in their 

 electric resistance, which in turn is caused to increase or 

 diminish a current through a telephone or telegraphic 

 relay generated by a local battery. To this type belong 

 the well-known coherers of Branly, Lodge, and Marconi, 

 which require tapping or rotating to bring them back con- 

 tinually to a condition of sensitiveness. 



Coherers, however, have been devised which require no 

 tapping. Thus it has been found by Mr. L. H. Walter 

 that if a short length of very fine tantalum wire is dipped 

 into mercury there is a very imperfect contact between the 

 mercury and tantalum for low electromotive forces. This 

 may perhaps arise from the fact that tantalum, like iron, 

 is not wetted by mercury. If, however, feeble electric 

 oscillations act between the mercury and tantalum, the 

 contact is improved whilst they last. If, then, the 

 terminals of a circuit containing a telephone in series with 

 a shunted voltaic cell are connected to the mercury and 

 tantalum respectively, and if damped or intermittent trains 

 of electric waves fall on an antenna and excite oscillations 

 which are allowed to act on the mercury-tantalum junc- 



d Tosi's Radiogoniometers for Directive Radioiel^graphy. 



tion, then at each train the resistance of the contact falls, 

 the local cell sends current through the telephone and pro- 

 duces a short sound, and if the trains come frequently 

 enough this sound is repeated and will be heard as a con- 

 tinuous noise in the telephone (Fig. 15). This sound can 

 be cut up into dot and dash signals by a key in the 

 sending instrument. If the transmitter is sending per- 

 sistent oscillations, then some form of interrupter has to 



