Investigation of the Simple Coherer. 295 



distances as well as of the forces involved. The Aphometer 

 is less. delicate in action, is not concerned with smiill distances, 

 but is an incomparably better instrument for determining 

 forces and is more under control. 



The Simple Coherer alone has been used, the idea being to 

 reduce the problem of coherence to its simplest possible 

 terms. Yet the results obtained are involved and complex, 

 so much so that it seems as though it would be hopeless to 

 expect a satisfactory and full explanation of coherence to 

 'crystallize out'' from a study of the usual complex coherer. 

 For in the Simple Coherer, at any rate, the conditions at one 

 contact can be fairly well kept constant or varied at will. As 

 much cannot be said of the ordinary coherer. 



To mention some chief points in conclusion : — 



I. The insulating layer between the surfaces of the contact 

 is of importance before the first coherence has occurred. It 

 has been shown that a condensed-air layer might produce all 

 the well-known resistance, at any rate in many cases, in my 

 investigations. Oxide as such asserts itself when strong- 

 currents pass with certain easily oxidized metals, but this is a 

 special case and does not affect the statement above. 



II. The term bridge has been used throughout to 

 express the region between one metal and the other. Even 

 if, as some may suppose, the metal surfaces merely compress 

 one another so as to touch over a small area (calculated in 

 section 3), and there is actually no length to the bridge ; 

 still, it is necessary to have some term to represent the 

 narrow space, call it a doorway, into which the current is 

 compressed in going from wire to wire. Whether it more 

 resembles a narrow bridge or a doorway, its strength is un- 

 mistakable as the tables in this paper will show. 



There actually is a bridge in certain cases which have been 

 pointed out — but they may be exceptions or they may not. 



III. The (molecular) change called in thi;3 paper orienta- 

 tion seems the most interesting fact brought to light. It 

 should have an important influence on our conceptions of 

 molecules and their relations to currents. The observations 

 of Prof. Bose, already referred to, seem to point in the same 

 direction. 



Some curious stray phenomena noticed during the research 

 have been mentioned ; others have been omitted, but are 

 none the less interesting. Of the problem of coherence 

 itself, many of the facts are left, so to speak, in the raw 

 state. There is, quite obviously, a great deal of work vet 

 to be done on the subject. 



