Investigation of the Simple Coherer. 



279 



6 C. Strong and Weak Currents. 



Having the wires freshly cleaned, if the spark-gap is put, 

 say 40- cm. (*'. e. comparatively far) from the contact, then 

 on producing a spark a weak current, say 0*001 ampere, will 

 refuse to pass the contact, and no coherence will occur. But 

 repeat the operation with the resistance in the circuit reduced 

 so that the current, if it passed, would be a large one, say 

 0*02 ampere, then coherence does occur, and the current 

 passes. On proceeding with the observations, two things 

 will be noticed : (1) coherence becomes greater at each fresh 

 trial with the strong current ; (2) coherence now occurs always 

 for a weak current. 



Thus a strong current seems to prepare the contact in some 

 way both for coherence and for the easy passage of a weak 

 current. See Table IX. 



Table IX. 





Resistance 











Radiation. 



in Contact 

 Circuit. 



Ammeter. 



Voltmeter. 



R.T. 



R.C. 



One spark . 



1050 



H 



001 



520 



530 



One ,, 



150 



32 



0-13 



)9 



530 



One 



50 



88 



0-27 



5 , 



600 



One ,, 



j) 



J5 



>} 



5) 



660 



Without „ 



)! 



») 





J) 



530 



One 





.'5 



,, 



)) 



800 



Without „ 



>5 







„ 



530 



One 





} 



M 





730 



Without „ 



1050 



H 



001 



„ 



530 



One 



) ? 





>> 



}> 



800 



One „ 





!> 



?> 



" 



800 



6 D. Direction of Discharge and of Current. 



Another relation observed was between the direction of the 

 contact-current and of the discharge ; the latter was seen by 

 attaching a Geissler tube to the terminals of the Ruhmkorff. 

 It was found that when the direction of the discharge agreed 

 with that of the current, coherence was much greater than 

 for opposition. This is shown in Table X. and curve (p. 281). 



The curve is easily understood ; the four highest peaks 

 are obtained when radiation and circuit-current agree ; the 

 other peaks, five in number, are produced when 11 and C are 

 opposite. 



