480 Prof. J. A. Fleming. Conversion of Electric [Jan. 24, 



does not obey Ohm's law, but the current increases to a maximum and 

 then slightly decreases as the voltage progressively increases. The 

 form of oscillation transformer employed with the device is as follows : 

 A small air-core induction coil has a primary circuit, which consists of 

 52 turns of gutta-percha covered wire, wound in a helical groove cut 

 on an ebonite rod 0*5 inch in diameter and 6 inches in length. The 

 primary circuit is made of a No. 20 or No. 22 S.W.G. copper wire. 

 The secondary circuit consists of 36,000 turns of fine silk-covered wire, 

 No. 36, wound in six coils, each having about 6000 turns, and all 

 joined in series. This secondary circuit has one terminal connected to 

 one common terminal of the galvanometer and the other to the common 

 terminal of the two oscillation valves (see fig. 4). The primary coil of 

 this oscillation transformer has one terminal connected to earth and the 

 other to a long insulated rod which acts as an aerial or electric wave 

 collector. To prevent the direct action of the transmitter upon the 

 secondary coil by simple electromagnetic induction, it is best to wind 

 the secondary coil in two equal parts in opposite directions and to 

 wind the primary in a corresponding manner. 



If an electric wave sent out from a similarly earthed transmitter 

 falls upon the rod, then an electrical oscillation is set up in the 

 receiving circuit and therefore in the primary coil of the oscillation 

 transformer inserted in series with it. This oscillation is raised in 

 voltage by the secondary coil of the transformer, and by reason of the 

 unilateral conductivity of a vacuum valve, placed in series with the 

 coil, one part of the oscillation, viz., the positive or the negative 

 current, passes round the galvanometer coils and affects it. 



If we employ a sensitive dead beat galvanometer of the type called 

 by cable engineers a "Speaking Galvanometer," then intelligible 

 signals can be sent by making small and larger deflections of the 

 galvanometer corresponding to the dot and dash of the Morse alphabet ; 

 anyone who can " read mirror " can read off the signals as quickly as 

 they can be sent on an ordinary short submarine cable with this 

 arrangement. 



The arrangement, although not as sensitive as a coherer or magnetic 

 detector, is much more simple to use. Also it has one great advantage, 

 viz., that it enables us to examine the behaviour of any particular form 

 of oscillation producer. By means of it we can detect changes in the 

 wave-making power or uniformity of operation of the transmitting 

 arrangement, by the variation of the deflection of the galvanometer. 

 Thus, for instance, if a spark-ball transmitter is being employed and 

 the deflection of the galvanometer in association with the receiving 

 aerial is steady, if we put the slightest touch of oil upon the spark-balls 

 of the transmitter, their wave-making power is increased and the 

 deflection of the galvanometer at once increases. Since the current 

 through the galvanometer is the result of the groups of oscillations 



