WITHOUT WIRES. 291 



from the other, but they are clearly and distinctly heard when the 

 ear is applied to the telephone. 



" The value of the system had been proved upon an occasion 

 when telegraphic communication was interrupted between the 

 island of Mull and the mainland, the post office telegrams being 

 transmitted by this method across the Sound of Mull. Mr. Preece 

 explained that the difficulty upon that occasion had been no 

 greater than then in the lecture theatre, for the law that had been 

 elicited demanded only that a length of wire should be used equal 

 to the distance over which it was required to send the signals. 

 Experiments had been carried out at a lightship on the Goodwin 

 Sands with the object of transmitting the signals through water, 

 but these had proved fruitless. Water being a conductor, it had 

 acted as a screen, interfering electrical currents being developed in 

 it, while the hull of the ship had also interfered. 



" A description was now given of Marconi's system. Marconi, 

 a pupil of Righi, had, one might say, gone back to first principles. 

 He employed the radiant energy emitted by a spark passing 

 through a series of four solid brass spheres. Of these four the 

 middle pair are larger than the outside two, from which they are 

 separated by air, they themselves being separated from each other 

 by a thin layer of oil. The principle known as Righi's is based on 

 the fact that solid brass spheres are twice as effective as hollow 

 ones — one of the few results arrived at in the first instance by 

 mathematical investigation. To receive the impression of the rays 

 emitted in this way an apparatus is used, the principle of which 

 depends upon the fact that under the influence of these rays a 

 small quantity of metal dust, consisting of 96 parts of nickel and 

 4 of silver, with a minute trace of mercury, becomes polarised and 

 acts as a conductor, joining the ends of a pair of wires, between 

 which it is placed in a glass tube. A current thus passes which 

 puts a relay in action, and a hammer is made to tap the glass tube. 

 The effects of this are two — namely, to give a signal representing 

 either a dot or a dash, as in the Morse system, and, moreover, to 

 shake down the adhering dust, now again depolarised, and so 

 interrupt the current. The results obtained by this method are 

 even more surprising than those of the method first described. 

 At its first trial on Salisbury Plain it was made to act at a distance 



