878 Dr. W. H. Eccles on Coherers. 



term subtracted from W. It may be mentioned again that 

 the absolute value of the multiplier of W in the above 

 equations is rather doubtful, because of the big extrapolation 

 necessary in calibrating the telephone. But doubt on this 

 point does not affect the character of the curves ; it affects 

 only their gradient. As written above, the approximate 

 equations for the curves suggest that for a particular de- 

 tector under invariable conditions there is a fixed wastage of 

 oscillation energy amounting constantly to about one-tenth 

 of an erg per second, however large or small the oscillation 

 energy given to the detector may be. If, however, the 

 equations be written 



w + 0'022 xlO- 8 = 0-024W and zu + 042 x 10" 8 = 0-019W, 



the inference is that a small quantity of energy, which is 

 invariable while the detector is undisturbed, is delivered by 

 the detector to the telephone circuit in a form that never 

 makes any proportion of itself manifest as sound. Whatever 

 the cause of this small energy wastage may be, the curves of 

 fig. 3 show that the coherer must be put amongst those 

 detectors that have been called "" integrating " detectors. 

 Thus the coherer is not, as has usually been supposed, a 

 " voltage-operated " detector. As detectors go, it has a very 

 good efficiency (i. e. ratio of energy conversion), but evidently 

 its efficiency falls rapidly as signals get weak. 



The curves of fig. 2 show how the sound heard in the 

 telephone varies with alteration of the potential difference 

 applied to the coherer and telephone in series. Each curve 

 is obtained by submitting the coherer to the fixed excitation 

 whose value in watts is marked on that curve. As the 

 excitation diminishes the maxima accompanying variation of 

 applied voltage become less marked. The resistance of the 

 coherer was kept as constant as might be during these experi- 

 ments, but wide variations of resistance are inevitable. The 

 asymmetry of the coherer under positive and negative voltages 

 shown in these curves obtained by the action of electrical 

 oscillations on the instrument, is no doubt connected with the 

 similar phenomenon mapped in fig. 4, where typical steady 

 current curves, plus and minus, are drawn. In these curves the 

 abscissa? are the potential differences applied at the terminals 

 of the coherer. In both cases the lack of symmetry is due 

 to the use in the coherer of two metals so different as iron 

 and mercury. In order to examine whether this asymmetry 

 was responsible for the failure of the curves of fig. 3 to pass 

 through the origin, a new series of experiments on a different 

 form of iron-oxide coherer was undertaken. 



