CHAPTER VI 



PHYSICAL RESEARCHES CONTINUED 



The Theory oj Molecular Strain and, its Interpretations 



RECALL now from Chapter IV the receiver of the electric 

 waves, the ' radio-conductor ' of Branly (called ' Coherer ' 

 by Lodge, in terms of his simple and attractive thesis of 

 the fusing together of its metallic particles at their points 

 of contact by the inductive action of the electric waves). 

 Next recall the difficulties and irregularities of its action, 

 more or less felt by all observers, and notably abated by 

 Bose's form of receiver. Bose, as we have seen, succeeded 

 in making his electric wave receiver, at first made of steel 

 springs (afterwards electroplated with cobalt to avoid 

 oxidation), highly reliable. He was also able to devise 

 other receivers which, in addition to their extreme sensitive- 

 ness, exhibited automatic recovery. He could exalt the 

 sensitiveness of his receivers to any degree desired by slight 

 increase of pressure of contact, and by increase of electro- 

 motive force in the receiving circuit. But after these 

 improvements a new anomaly appeared. When experi- 

 ments had been carried on continuously for a couple of 

 hours or so, the receiver became less sensitive, and after 

 more prolonged work, still more so, reminding one of 

 fatigue. What could be the meaning of this fatigue ? 

 When the fatigued receiver was allowed to rest for several 

 hours, it became sensitive once more. Thinking, naturally 

 enough, that longer rest would render it still more sensitive, 

 Bose left the receiver aside for several days, with the quite 



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