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Mr. P. E. Shaw : 



10. Various Metals and Carbon. 



All the work so far mentioned was done with a copper- 

 copper coherer ; we will now come to other combinations. 

 Complete observations of coherence were taken, but only 

 a table summarizing the results will be given. The phe- 

 nomena displayed are so diverse that it might almost be said 

 that every pair of metals behaved differently from every other 

 pair. 



It was interesting, in trying different combinations, to 

 watch for idiosyncrasies, as one had ever new and peculiar 

 effects. 



Coherence for direct current is abbreviated to C.D.C. 

 „ „ radiation „ „ „ C.R. 



One, two, or three stars in a column shows whether the 

 effect is weak, strong, or very strong respectively. 



This table shows : — 



(1) The general principle of the important role which 

 oxide plays at the contact — for all the more oxidizable metals 

 show such rapid oxidation of the contact that no coherence 

 will take place after a few "makes" and " breaks " ; then a 

 new place has to be chosen on the wires. Moreover, 

 platinum-platinum, the least oxidizable of all cases, shows 

 wonderful cohering power. 



(2) A fluttering, lasting for many minutes, occurs in the 

 voltmeter readings when the current is weak in the c:ise of 

 some metals. This is a noteworthy peculiarity, it certainly 

 does not occur as a rule. 



Now since the pressure of the wires on one another is 

 constant and vibrations are excluded, we must infer that 

 some (molecular ?) breakdown and recovery are going on at 

 the contact. It is only found for weak currents and is most 

 pronounced in the alloys, platinoid and manganin. The 

 current seems to be "critical," more current would break 

 down opposition and give the molecules a permanent "set"" 

 or orientation, while less current would be quite ineffective. 



(3) Evidence of some fragile bridge certainly for 

 graphite-fusemetal and platinum-platinum. 



If pressure was increased in these cases, but not apparently 

 in others, the bridge between the surfaces seems to have been 

 crushed and coherence destroyed. 



(4) Lead seems to make contact in a remarkable way : 

 each time the wires touched, a singular noise, like a creaking 

 door-hinge, was heard in the telephone of the contact circuit. 



