( m^ ) 



Physics. — "^h/ /lie liijiiwiicc of electric tvaDes upon platinurii 

 nnrrors. [Coherer action).'' \iy Dr. .1. Clay. (Coiiimiinicated by 

 Prof. H. Kamerlingh Onnes). 



(CommiinicakHl in tlie meeling of Dr^ccmber 24, 1910), 



In llio present paper T give the results of some of 1113' experiments 

 undertaken with a view to solving a difticulty regarding coherer 

 action on platinum mirrors wliicli, to the best of my knowledge, 

 has not yet been cleared up. Various observers^) have noticed that 

 electric waves falling upon a plalinuni mirror cause an inci'case of 

 ils electrical resistance. This was difticull to reconcile wil h Lodck/s'^) 

 assumption that clecti-ic oscillations render the metallic |»arlicles of 

 a cohei-er beller able to conduct electricity. 



It ap[)eared to me that the intluence of electric oscillations depended 

 a great deal upon circumslances. I had sevci-al platinum miri-ors 

 construclcd, which were not all raised to the same temperature, so 

 that the platinum layer was not of the same firmness in every 

 case. Miri-ors N". 1 and 2 (see Table) were heated to about 300°, 

 and 3, 4, and 5 to about 400°. N". H was a lube platinised on the 

 inner side so that the platinum could not be tirmly fused into the 

 glass. N". 7 was a tube platinised on the outside l\y being ke|)t for 

 a long time at red heat; from it platinum could not be removed 

 even with a sharp instrument. 



From the table the influence of electric waves upon the various 

 mirrors can be seen ; in 1 and 2 it is greatest, in 3, 4, and 5 it is 

 much less, in 6 it is again great, wdiile in 7 it vanishes completely. 

 From this it appears that the magnitude of the change depends upon 

 the condition of the |)latiuum deposit, and points, therefore, to a 

 mechanical action. Particularly with 1 and 2, tapping after a change 

 had a strongly recuperative effect on the resistance. With N°. 2 a 

 change of 3 ohms was observed to be occasioned even by a hissing 

 noise. 



It was also ascertained that at large distances from the source of 

 the oscillations (the spark of an induction coil) the waves occasioned 

 a reduction of the resistance, at shorter distances, on the other hand, 

 they brought about an increase. It seems to me that the latter effect 

 may be regarded as analogous to the action of an electrostatic field 



1) AscHKiNAss. Verb. d. Phys Gesellsch. Berlin. 1894 and Wied. Ann. ï>7. Branly 

 La Lumière Electrique 40. 1891. Haga. Wied. Ann. 56. 1895. Mizuno Phil. Mag. 

 40. 1895. D. V. GuLTK. Diss. Groningen. 1896. Wied. Ann. 66. 1898. 



2) Lodge. The Work of Hertz and his Successors. 1894. 



