544 Intelligence and Miscellaneous Articles. 



blende, galena. The galena carries its silver generally in molecular 

 or isomorphous combinations, except in the case of rich ores, when 

 native silver and argentite appear sometimes as threads along the 

 cleavage-planes. 



In the effect of the country-rock on ore-deposition, the chief 

 factors have been: (1) the physical character of the rock and the 

 consequent natnre of the fissure, (2) its porosity, and (3) its chemical 

 composition. The process of deposition involves interchange of 

 constituents between rock and solutions, even with the least soluble 

 rocks. 



Ore-deposition has persisted over a vertical range of 5000 -to 

 6000 feet, of which over one-half has been shorn off by denudation. 

 The effects of secondary processes have been exerted to depths of 

 over 600 feet. The main points in the work are supported by 

 field-observations, and by the results of microscopic and chemical 

 research. 



3. ' The Vertebrate Fauna found in the Cave-Earth at Dog Holes, 

 Warton Crag (Lancashire).' By John Wilfrid Jackson, F.G.S., 

 Assistant Keeper in the Manchester Museum. 



LVII. Intelligence and Miscellaneous Articles. 



To the Editors of the Philosophical Magazine. 



n Cavendish Laboratory, Cambridge, 



Gentlemen,- Aug> 9th? ^ 



T^f ITH reference to the paper in your last issue by Mr. Jeans 

 ' ' on the motion of an electrified particle near an electrical 

 doublet, and its bearing on the theory of radiation given by me in the 

 June number, I should like to state that I was quite aware that the 

 state of steady motion I considered would not be permanent. As 

 a matter of fact I showed in the paper that if the particle suffered 

 a radial displacement from its circular orbit, no force acted upon 

 it tending to bring it back to its former position or to drive it 

 still further away; thus if the particle were started with a radial 

 velocity it would slowly drift from its state of steady motion. 

 I did not then, nor do I now, consider this fact of any import- 

 ance with respect to the theory of radiation I was discussing, 

 for there is nothing in that theory which requires these systems to 

 be permanent. All that is necessary is that, at any time, there 

 should be a number (infinitesimal in comparison with the number 

 of molecules) of such systems which remain in this state, or only 

 depart slightly from it, in the time occupied by a few vibrations of 

 ultra-violet light. 



Yours very sincerely, 



J. J. Thomson. 



