1897.] on tJie Polarisation of the Electric Bay. 297 



pose that the uncertainty in the response of the receiver is probably 

 due to the following : — 



(1) Some of the particles of the coherer might be too loosely 

 applied against each other, whereas others, on the contrary, might be 

 jammed together, preventing proper response. 



(2) The loss of sensibility might also be due to the fatigue pro- 

 duced on the contact surfaces by the prolonged action of radiation. 



(3) As the radiation was almost entirely absorbed by the outer- 

 most layer, the inner mass, which acted as a short circuit, was not 

 necessary. 



For these reasons I modified the receiver into a spiral-spring 

 form. Fine metallic wires (generally steel, occasionally others, 

 or a combination of different metals) were wound in narrow spirals 

 and laid in a single layer on a groove cut in ebonite, so that 

 the spirals could roll on a smooth surface. The ridges of the 

 contiguous spirals made numerous and well-defi.ned contacts, about 

 one thousand in number. The useless conducting mass was thus 

 abolished, and the resistance of the receiving circuit almost entirely 

 concentrated at the sensitive contact surface exposed to radiation. If 

 any change of resistance, however slight, took place at the sensitive 

 layers, the galvanometer in circuit would show strong indications. 

 The pressure throughout the mass was made uniform as each 

 spring transmitted the pressure to the next. When the contact 

 surfaces had too long been acted on, fresh surfaces could easily be 

 brought into contact by the simultaneous rolling of all the spirals. 



The sensibility of the receiver to a given radiation, I found, 

 depends (1) on the pressure to which the spirals are subjected, and 

 (2) on the E.M.F. acting on the circuit. The pressure on the spirals 

 may be adjusted, as will be described later on, by means of a fine 

 screw. The E.M.F. is varied by a potentiometer-slide arrangement. 

 This is a matter of great importance, as I often found a receiver, 

 otherwise in good condition, failing to respond when the E.M.F. 

 varied slightly from the proper value. The receiver, when subjected 

 to radiation, undergoes exhaustion. The sensibility can, however, 

 be maintained fairly uniform by slightly varying the E.M.F. to keep 

 pace with the fatigue produced. 



The receiving circuit thus consists of a spiral-spring coherer, 

 in series with a voltaic cell and a dead-beat galvanometer. The 

 receiver is made by cutting a narrow groove in a rectangular piece 

 of ebonite, and filling the groove with bits of coiled spirals arranged 

 side by side in a single layer. The spirals are prevented from falling 

 by a glass slide in front. They are placed between two pieces 

 of brass, of which the upper one is sliding and the lower one fixed. 

 These two pieces are in connection with two projecting metallic rods, 

 which serve as electrodes. An electric current enters along the 

 breadth of the toj) spiral and leaves by the lowest spiral, having 

 to traverse the intermediate s^)irals along the numerous points of 

 contact. When electric radiaticJn ic, absorbed by the sensitive sur- 



