August 27, 1909] 



SCIENCE 



265 



interesting example of the way nature re- 

 sponds to the demands made upon her by 

 mathematicians. Some years before the 

 discovery of corpuscles it had been shown 

 by a mathematical investigation that the 

 mass of a body must be increased by a 

 charge of electricity. This increase, how- 

 ever, is greater for small bodies than for 

 large ones, and even bodies as small as 

 atoms are hopelessly too large to show any 

 appreciable effect; thus the result seemed 

 entirely academic. After a time corpuscles 

 were discovered, and these are so much 

 smaller than the atom that the increase in 

 mass due to the charge becomes not merely 

 appreciable, but so great that, as the ex- 

 periments of Kaufmann and Bucherer 

 have shown, the whole of the mass of the 

 corpuscle arises from its charge. 



We know a great deal about negative 

 electricity ; what do we know about positive 

 electricity? Is positive electricity molecu- 

 lar in structure 1 Is it made up into units, 

 each unit carrying a charge equal in magni- 

 tude though opposite in sign to that carried 

 by a corpuscle ? Does, or does not, this unit 

 differ, in size and physical properties, very 

 widely from the corpuscle 1 We know that 

 by suitable processes we can get corpuscles 

 out of any kind of matter, and that the cor- 

 puscles will be the same from whatever 

 source they may be derived. Is a similar 

 thing true for positive electricity ? Can we 

 get, for example, a positive unit from oxy- 

 gen of the same kind as that we get from 

 hydrogen? 



For my own part, I think the evidence is 

 in favor of the view that we can, although 

 the nature of the unit of positive electricity 

 makes the proof much more difficult than 

 for the negative unit. 



In the first place we find that the positive 

 particles— "canalstrahlen" is their tech- 

 nical name— discovered by our distin- 

 guished guest, Dr. Goldstein, which are 

 found w'hen an electric discharge passes 



through a highly rarefied gas, are, when 

 the pressure is very low, the same, what- 

 ever may have been the gas in the vessel to 

 begin with. If we pump out the gas until 

 the pressure is too low to allow the dis- 

 charge to pass, and then introduce a small 

 quantity of gas and restart the discharge, 

 the positive particles are the same what- 

 ever kind of gas may have been introduced. 



I have, for example, put into the ex- 

 hausted vessel oxygen, argon, helium, the 

 vapor of carbon tetrachloride, none of 

 which contain hydrogen, and found the 

 positive particles to be the same as when 

 hydrogen was introduced. 



Some experiments made lately by Wel- 

 lisch, in the Cavendish Laboratory, strongly 

 support the view that there is a definite 

 unit of positive electricity independent of 

 the gas from which it is derived; these ex- 

 periments were on the velocity with which 

 positive particles move through mixed 

 gases. If we have a mixture of methyl- 

 iodide and hydrogen exposed to Rontgen 

 rays, the effect of the rays on the methyl- 

 iodide is so much greater than on the 

 hydrogen that, even when the mixture 

 contains only a small percentage of methyl- 

 iodide, practically all the electricity comes 

 from this gas, and not from the hydrogen. 



Now if the positive particles were merely 

 the residue left when a corpuscle had been 

 abstracted from the methyl-iodide, these 

 particles would have the dimensions of a 

 molecule of methyl-iodide; this is very 

 large and heavy, and would therefore move 

 more slowly through the hydrogen mole- 

 cules than the positive particles derived 

 from hydrogen itself, which would, on this 

 view, be of the size and weight of the light 

 hydrogen molecules. Wellisch found that 

 the velocities of both the positive and nega- 

 tive particles through the mixture were the 

 same as the velocities through pure hydro- 

 gen, although in the one case the ions had 

 originated from methyl-iodide and in the 



