1880.] On some Thermal Effects of Electric Currents. 409 



encouraging, when the microphone transmitter M was spoken into. 

 The articulation, though muffled, was clear, and words could easily 

 be heard. 



1. Experiments were first made to determine the length which gave 

 the loudest sound and the clearest articulation, and, after repeated 

 trials with every variation of length from one inch to six feet, it was 

 found that a wire six inches long gave the maximum effect. 



2. Experiments were then made to determine the diameter of the 

 wire that gave the best effect, and after repeated trials with every 

 gauge drawn from 0*0005 inch to 0*005 inch, it was found that wire of 

 the diameter 0*001 inch gave the best effect. 



3. Experiments were then tried with wires six inches in length and 

 0*001 inch diameter of different materials, viz., gold, iron, aluminium, 

 silver, copper, palladium, and platinum, and they came out in the 

 following order of merit : — 



Platinum Very clear. 



Aluminium Very variable. 



Palladium Clear. 



Iron Clear. 



Copper Faint. 



Silver Faint. 



Gold Very poor. 



4 The effect of mechanical strain was tried. It was found not to 

 vary the effect. When once the requisite tension, which varied with 



