Dr. W. H. Eccles on Coherers. 887 



remarkable and the difficulty of carrying a coherer through 

 a variety of experiments without altering its internal state 

 is so great, that full confirmation will only be attained 

 by selection of the best from a very large number of 

 observations. 



I have to thank the Royal Society's Government Grant 

 Committee for a grant of money to defray the cost of con- 

 struction of the apparatus used in the above experiments. 



Summary . 



A method of investigating detectors is developed with 

 special reference to the relations between the energy given 

 to the detector in the form of electrical vibrations and the 

 energy delivered by the detector, as direct current, to the 

 circuit of the indicating instrument. The stream of energy 

 supplied to the detector was always of the same order as that 

 usual in telegraphy. The detector under examination was 

 placed in a circuit containing suitable inductance and capacity, 

 which was secondary to a primary circuit. The primary could 

 be set into electrical vibration by breaking a known current 

 in it. The coupling was very small, so that when a current 

 of a few milliamperes was broken in the primary, the energy 

 delivered to the detector was of the order a thousandth of an 

 erg, and the electromotive force at the coherer terminals was 

 of the order a tenth of a volt. The response of the detector 

 was measured by comparing the sound in its telephone with 

 the sound produced in the same telephone by interrupting a 

 measurable direct current. A special switch key enabled 

 the comparison to be made quickly. The power delivered 

 to the detector and to the telephone was determined by 

 extrapolation from measurements on stronger currents with 

 the thermogalvanometer. 



The results of experiments on coherers made of oxidized 

 iron wire dipping into mercury, and on coherers made of a 

 clean iron point touching an oxidized iron plate, are exhibited 

 as curves connecting : (1) the steadily applied E.M.F. and 

 consequent current through the coherer; (2) the steadily 

 applied E.M.F. and the power given to the telephone, for 

 various rates of delivery of vibration energy to the detector ; 

 (3) the power delivered to the detector and the power passed 

 to the telephone, the E.M.F. applied to the coherer being 

 constant. Curves (1) show that in a self-restoring coherer 

 the current increases more and more rapidly as the E.M.F. 

 is raised, till, in general, a point of inflexion is reached, and 

 then the current increases more slowly. Curves (2) show 



