432 



THE POPULAR SCIENCE MONTHLY 



neutral molecule, are thrown instantly to the plates M and N, their 

 speeds in the field here used being something like five or ten thousand 

 centimeters per second; but, when the field is ofE, these ions remain in 

 the air between the plates, and, sooner or later, as their number increases, 

 one or more of them comes into contact with a drop and sticks to it. 

 If we look now at the changes which occurred in the experiment 

 recorded, we see that the first change in the time in the field, namely, 

 that from 12.45 to 21.85, represented the advent upon the drop of 2 

 unit charges, since the 16-second time which is found later in the table 

 was skipped in this catch. All the other changes in the table, save one, 

 namely, that from 34.8 to 16.0, represented the advent of single charges, 

 and this one represents again the advent of a double charge since the 

 21.9 second speed was here skipped. This indicates that there are 

 probably no ions which have a very large number of units of excess of 

 one kind of electricity upon them, but it gives us no information as to 

 whether the act of ionization consists in the detachment of only one 

 elementary electrical charge from a neutral molecule, or of two or 

 three; for, so long as the changes are occurring when the field is off, it 

 is impossible to distinguish between the capture of a single ion carrying 

 two or three units of charge, and the successive capture of two or three 

 ions each carrying the unit charge. 



It was necessary, therefore, to catch the ions at the very instant of their 

 formation, or better, to catch a molecule in the very act of splitting up 

 into ions. Accordingly, the experiment was modified as follows. By suit- 

 ably adjusting the PD between the plates M and N, it was found possible 

 to hold a minute positively charged drop suspended, like Mohammed's 

 coffin, as long as desired between heaven and earth, that is, in this case 

 between M and N, the downward pull of gravity being exactly neutral- 



j30cm- 



\covti\ 



U M - 



■Si 



-+- 



N ±_ 



9 o-fo~o^|i|i|i|i|i|ih 



t 



^ 



T 

 ibcm 



Edrth 



Fig. 3. 



ized by the upward pull of the field. Having obtained a drop in this 

 position, there was produced beneath it a sheet of X-ray ionization in the 

 manner shown in Fig. 3, so that when the X-ray bulb was excited, the 

 drop was in a veritable shower of the charged positive residues of the 

 molecules broken up by the X-rays. Now, if two or more electrons were 



