Investigation of the Simple Coherer. 



291 



being produced at the spark-gap near at hand, then we shall 

 be able to observe, by listening in the telephone, whether any 

 discharge or coherence occurs at the contacts «r, y. The 

 same process may be continued when the surfaces just touch, 

 or when, going further, they press one another hard. 

 Suppose coherence occurs when the surfaces are, say 

 5 x 10~ 7 cm. apart, then on drawing x away, y will hold to it 

 for a small distance, but severance must occur, the surfaces 

 being now, say 1 x lO -6 cm. apart ; the difference between 

 these two distances will provide some information as to the 

 force of coherence. We can also find what is the limiting 

 distance at which coherence will occur, whether any bridge 

 is formed, and we can look for orientation, &c. 



Tt is evident that in such an arrangement we have a 

 valuable auxiliary means of examining coherence problems. 



As in the last section the observations, except for three short 

 tables, will be curtailed to a mere table summarizing the 

 results. 



Two stars show when the effect is a pronounced one. 



Combinations. 



Copper-Copper 



Copper-b use-metal ... 



Copper-Iron 



Copper-Carbon 



Copper-Plat inism 



Carbon-Platinum ... 



Carbon-Carbon 



Platinum-Iridio- 

 platinum 



C.D.C. 





C.R. 



Bridge 

 for C.R. 



Remarks. 



Small effects only. 



Large region of in-i 

 complete contact, j 



Distinct "fatigue" 

 shown. 



Cober- 

 ence. 



"Snap." 



Cober- 

 ence. 



Limit of 

 Striking. 



* * 



* 

 it * 



* 







* 



* * 



* * 

 

 





 



* 

 * 



12xlCr R cm. 



10xl0-tfcin. 

 8x10-6 cm. 



* 



* 

 * * 



Platinum -Platinum ... 



The following table was taken to ascertain the " striking " 

 distance for Copper-Copper and the effect of the coherence 

 on. the contact. By the striking distance is meant the 

 greatest distance of separation of the contacts with which 

 coherence can be produced by radiation from the given 

 source at a known distance. 



