Dr. W. H. Eccles on Coherers. 875 



Finally, by observation of the therm ogalvanometer de- 

 flexion when a primary current of y 1 ^ ampere was interrupted 

 168 times a second, the result was established that with the 

 primary and secondary in their standard relation a quantity 

 of energy amounting to very approximately 4*82 x 10 -11 joule, 

 or about 0*0005 erg, is passed to a detector of 1000-ohms 

 resistance at each break of a primary current of 0*01 ampere. 

 This corresponds to a power-delivery of 0*01 erg per second 

 when the interrupter is running at the standard frequency. 

 Corresponding figures were obtained for the cases where the 

 detector has different resistances between 100 ohms and 

 2000 ohms. 



In the actual experiments on detectors two things were 

 chosen for variation, namely, the electromotive force applied to 

 the detector and the oscillatory energy passed from the primary 

 to the detector. The effect observed was the loudness of the 

 sound in the telephone. The curves of fig. 2 (p. 876) have as 

 abscissas the varying external E.M.F. applied to the coherer, 

 and as ordinates the consequent effect in the telephone. Each 

 curve in the diagram is obtained by supplying to the coherer 

 the constant power marked on the curve. The curves in fig. 3 

 (p. 877) have as abscissae the power supplied to the coherer 

 when its applied E.M.F. is unvarying ; the ordinates are the 

 effect in the telephone. The telephone effect is plotted as 

 estimated power given by the coherer to the telephone circuit. 

 The numerical connexion between the power passed into the 

 telephone circuit and the measured intensity of the sound 

 in the telephone was determined as follows. The thermo- 

 galvanometer whs put in the telephone circuit in series with 

 the telephone, and a large primary current was interrupted 

 at the normal rate. The intensity of the loud sound in the 

 telephone was measured by the potential divider, and at the 

 same time a reading of the galvanometer deflexion was taken. 

 A resistance was then put in series with the telephone and 

 the galvanometer, and the measurements repeated. These 

 readings oive sufficient data to determine the amount of 

 energy being dissipated in the telephone when the intensity 

 of a sound is equal to that due to any assigned length of the 

 potential divider P 3 . The measurements thus made showed, 

 besides, that the power delivered by the detector to the thermo- 

 galvanometer and telephone was practically proportional to 

 the square of the length of P 3 required to produce equal 

 sounds in the telephone. It is rather a big extrapolation to 

 extend these results obtained with currents large enough to 

 affect the thermogalvanometer, to currents that give only 

 faint sounds in the telephone ; but if we do this, we find that 

 when the intensity of sound produced by a detector is equal 



