282 



SCIENCE 



[N. S. Vol. XXXIV. No. 870 



may be the result of the increased permea- 

 bility and oxidation. Perhaps the increased 

 oxidation in fertilized eggs caused by alkaline 

 NaCl is due to still further increase in perme- 

 ability to OH-ions. 



P. H. Mitchell 

 J. P. McClendon 

 Woods Hole, Mass., 

 August 11, 1911 



THEORIES OF ELECTRICAL DISCHARGE 



The present attitude of the scientific mind 

 on the one-fluid and the two-fluid theories is 

 amusingly similar to the conditions in the 

 early part of the last century concerning the- 

 ories of light. The emission theory and the 

 wave theory were both well known. Either 

 could be held by any one who chose to do so. 

 Either would serve as a means for explaining 

 phenomena. The emission theory had the ad- 

 vantage. It had come down through genera- 

 tions from a revered source. There is such a 

 thing as mental inertia. Presnel and Young 

 learned this. When they fully explained phe- 

 nomena on the theory of transverse vibrations 

 which could not be explained by the emission 

 theory, it had little effect. They devised new 

 experiments which could not be explained by 

 Newton's theory. They explained the phe- 

 nomena of Newton's rings on a rational basis. 

 It all counted for nothing. Newton's fol- 

 lowers might not be able to explain what it 

 was that happened when light had a fit of easy 

 transmission, or a fit of easy reflection. It 

 was, however, evident that the fits were there, 

 for Newton's rings gave evidence of it. 



Every one will of course admit that the two- 

 fluid theory has served a useful purpose. It 

 has, however, also led us astray. It has led 

 us to take a wrong view of phenomena. 



When it is said, for example, that hot metals 

 emit positive ions, the idea conveyed is very 

 different from that which would be conveyed 

 by the statement that hot metals take negative 

 corpuscles from the gas molecules which sur- 

 round them. 



If one were to say that householders all over 

 the country are emitting mail-carriers, the 

 idea conveyed would be definite and very mis- 



leading. As a matter of fact they are re- 

 ceiving their mail. The mail-carriers simply 

 bridge the gap between the conduction chan- 

 nels along the railways, and the householder. 

 Of course it is perfectly evident that posi- 

 tive ions such as exist in discharge through 

 gases can not circulate or flow through a 

 copper wire. They simply vibrate to and fro 

 between the terminals. The copper wire is 

 itself a solid aggregation of positive ions. 

 The negative corpuscles pass in rhythmical 

 transfer from molecule to molecule within the 

 wire. All of the phenomena of the vacuum 

 tube and of discharge across air gaps are 

 merely incidental to the condition that at that 

 point the conductor is in gaseous form. The 

 Faraday dark space is simply a region in 

 which molecules, supercharged in the region 

 of negative glow, are urged away from the 

 negative terminal, without appreciable inter- 

 change or transfer of the negative corpuscles 

 from molecule to molecule. 



The positive or luminous column is a region 

 in which this transfer is going on. These two 

 regions may exist side by side. A small wind- 

 mill made of non-conducting material is then 

 driven in opposite directions in the dark and 

 the luminous columns. The luminous col- 

 umns are simply " canal rays." The carriers 

 are returning after having delivered all of 

 their supercharge and part of their normal 

 charge. 



These dark and luminous regions may, 

 under proper conditions, exist as striations. 

 They are then electrically produced sound 

 waves. 



The positive terminal of an influence 

 machine is an exhaust terminal. Negative 

 corpuscles from the surrounding air are 

 drained into it. A disruptive discharge can 

 be made to end in such a drained region, as 

 " sheet lightning," before the positive terminal 

 is reached. 



Every lightning discharge which has its 

 terminals in air must at its positive end be a 

 region of " sheet lightning." It is probably 

 often at higher altitudes than the rain-clouds. 

 The negative end is usually within the clouds, 

 and that end is " forked lightning." 



