1897. 



on Signalling through Space without Wires. 



471 



r-4- 



i c 



^— WW- 



of tbe currents in the coiled cable, and the effects on board, though 

 perceptible, were very trifling — too minute for signalling. Previous 

 experiments had failed to show the extremely rapid rate at which 

 energy is absorbed with the depth or thickness of sea water. The 

 energy is absorbed in forming eddy currents. There is no difficulty 

 whatever in signalling through 15 fathoms. Speech by telephone 

 has been maintained tiirough 6 fathoms. Although this experiment 

 has failed through water, it is thoroughly practical through air to 

 considerable distances where it is possible to erect wires of similar 

 length to the distance to be crossed on each side of the channel. It 

 is not always possible, however, to do this, nor to got the requi- 

 site height to secure the best effect. It is impossible on a light- 

 ship and on rock lighthouses. There are many small islands — 

 Sark, for example — where it can- 

 not be done. 



In July last Mr. Marc(mi 

 brought to England a new plan. 

 My plan is based entirely on 

 utilising electromagnetic waves 

 of very low frequency. It de- 

 pends essentially on the rise and 

 fall of currents in the primary 

 wire. Mr. Marconi utilises elec- 

 tric or Hertzian waves of very 

 high frequency, and they depend 

 upon the rise and fall of electric 

 force in a sphere or spheres. He 

 has invented a new relay which, 

 for sensitiveness and delicacy, ex- 

 ceels all known electrical appa- 

 ratus. 



The peculiarity of Mr. Mar- 

 coni's system is that, apart from 

 the ordinary connecting wires of 

 the apparatus, conductors of very 

 moderate length only are needed, 

 and even these can be dispensed 

 with if reflectors are used. 



The Transmitter. — His trans- 

 mitter is Prof. Righi's form of 

 Hertz's radiator (Fig. 2). 



Two spheres of solid brass, 4 inches in diameter (A and B), are 

 fixed in an oil-tight case D of insulating material, so that a hemisphere 

 of each is exposed, the other hemisphere being immersed in a bath 

 of vaseline oil. The use of oil has several advantages. It main- 

 tains the surfaces of the spheres electrically clean, avoiding the 

 frequent polishing required by Hertz's exposed balls. It impresses 

 on the waves excited by these spheres a uniform and constant form. 



2 I 2 



Fig. 2. — Dingrara of tbe Marconi 

 apparatus. 



