280 



Mr. P. E. Shaw 



7. Dimensions of the "Bridge." 



Instead of considering the two wires forming the simple 

 coherer to be in actual metallic contact, suppose each wire to 



Table X. 



Radiation 

 direction. 



Current 

 direction. 



R.T. 



R.C 



2000 



Voltmeter. 



R.D. 



C.R. 



2800 



030 







„ 



2800 





R.D. 



C.R. 



*> 



2000 

 2800 



0-30 



R.D. 



CD. 



" 



1600 

 2800 





R.D. 



CD. 



J5 



1300 

 2800 



032 



R.D. 



C.R. 



" 



2400 

 2800 



0-28 



R.R. 



C.R. 



" 



1200 

 2800 



027 



R.R. 



C.R. 



" 



700 

 2800 



0-34 



R.R. 



CD. 



» 



2000 



2800 



0-19 



R.R. 



CD. 



)! 



2000 

 2800 



019 



have a layer of condensed gases over its whole surface. 

 Suppose that this layer is not all squeezed out when the wires 

 are brought together with the small pressures used in these 

 experiments. This layer remaining is very thin, but if it 

 does remain, as we suppose, it will produce a discontinuity 

 there, so that practically no current can pass. 



When, however, violent changes in the E.M.F. are pro- 

 duced across it, it will be pierced and a " bridge " of particles 

 may be formed between the metal surfaces. This bridge is 

 not formed of loose particles, but has the full strength of 

 solid metal ; so that, though very small, it has considerable 

 strength and stability, and as such might exhibit the forces 

 of coherence. 



As previously stated, the resistance of the contact could be 

 written down at any time ; thus, for example, take Table IX.; 

 the resistances after coherence range from 8co to 25&>, but if 

 R = resistance of " bridge" (say 10g>), 

 k= specific resistance (0*0000017 for copper), 

 1 = length of " bridge," 

 a = radius of area of contact, 



then 



B--M, 



