Experiments on Positive Rays. 221 



considerable number of types, for example in benzene vapour 

 I have counted seventeen different types of positive 

 carriers. 



Indeed, the splitting up of the gas by the electric discharge 

 is so complete that the photographs of the positive rays 

 obtained from the vapours of different hydrocarbons may be 

 almost identical. Thus, for example, the prominent lines for 

 the vapours of methyl alcohol, ethyl alcohol, ether (0 2 H 5 ) 2 0, 

 and dimethyl ether are identical, showing that the more 

 important rays are due to the products of: dissociation of the 

 molecules of these substances, and not to the undissociated 

 molecules ; the lines due to the latter, if they occur at all, are 

 exceedingly faint. 



On tlie Relative Brightness of the Lines on the photographic 

 plate as an index of the number of the Carriers -producing the 

 Lines. — It is necessary, however, to be very careful in drawing 

 any conclusion as to the number of carriers having any 

 particular value of e/m from the brightness of the parabola 

 corresponding to this value of e/m. When the kinetic 

 energy of the particles of different kinds is the same, the 

 photographic plate is much more sensitive to the lighter 

 carriers with a high velocity than to the slower and heavier 

 carriers. I had suspected that this was the case for some 

 time, but had no idea that the effect was so marked until 

 I compared the indications of the plate with those of a 

 Faraday cylinder. 



The details of the apparatus used for the Faraday 

 cylinder will be described later : it will be sufficient to say 

 here that they were such that the particles forming the 

 different pnrabolas could be driven in succession into the 

 Faraday cylinder, and the charges they communicated to ifc 

 in a given time measured. As these charges (when the 

 particles only carry one unit charge) are proportional to the 

 number of particles entering the cylinder, the indications 

 of the Faraday cylinder will give the number of the different 

 kinds of particles. For example, when the gas in the 

 discharge- tube was the residual gas left after the air was 

 pumped out, the lines on the photographic plate due to the 

 hydrogen atom and the molecule were very much brighter 

 than that due to the oxygen atom, and the line due to 

 the hydrogen atom than that due to the molecule. The 

 experiment with the Faradny cylinder showed, however, that 

 there were many more atoms of oxygen than of hydrogen, 

 and also that there were more hydrogen molecules than 



Q2 



