278 ANNUAL REPOET SMITHSONIAN INSTITUTION, 1910. 



This elementary charge has been susceptible of measurement. It 

 is easy to evaluate the quantity of electricity necessary to liberate a 

 gram of matter — for example, a gram of hydrogen in the electrol- 

 ysis of water — and thus to obtain the total charge of the hydrogen 

 ions. These ions correspond to the molecules, and as the number of 

 molecules in a gram of hydrogen is known, the charge carried by a 

 single ion may be determined. This charge is very minute; it 

 amounts to 4.10-^" in terms of the C. G. S. electrostatic unit. 



The study of the radiations obtained in rarified gases has also 

 been of assistance in making our knowledge of the atom of electricity 

 more definite. Wlien an electric discharge is produced in a gas by 

 means of a static machine or an induction coil under ordinary pres- 

 sure a disruptive spark is obtained. In a tube where the pressure is 

 reduced the aspect of this spark is changed and when the pressure 

 is not more than a few millionths of an atmosphere (Crookes's vac- 

 uum) a ray emanating from the cathode (negative pole) may be 

 observed. Whatever may be the position of the anode or positive 

 pole, this cathode ray is emitted perpendicularly to the surface of 

 the cathode and is sent out in a straight line. The glass of the tube 

 where the radiation strikes it takes on a beautiful green fluores- 

 cence. These cathode waves excite phosphorescent bodies ^ and heat 

 screens placed in their path. 



These rays emanating from the cathode bear the name of cathode 

 rays. They were discovered in 1869 by Hittorf, and have since been 

 made the subject of study by a gi-eat many physicists, among whom 

 are Crookes, J. J. Thomson, Jean Perrin, Marjorana, Lenard, Wien, 

 Villard, and others. Sir William Crookes was the first to propound 

 the hypothesis that they were due to a fourth state of matter, the 

 radiant state, which took shape as a molecular bombardment, as it 

 might be called. This truly remarkable idea met with much in- 

 credulity, as at that period (1880) the tendency of most men of 

 science was to attribute all such phenomena to a vibratory move- 

 ment and not to a flow of matter itself. Many physicists, therefore, 

 considered the cathode rays to be due to nndulatory movements 

 analagous to light. This interpretation was soon to be abandoned, 

 however. Later experiments confirmed in the most startling man- 

 ner the ideas of Sir William Crookes, subject only to the qualification 

 that the radiant state was due in the cathode rays not to a bombard- 

 ment of particles of matter, but to a bombardment of electrified cor- 

 puscles which were much smaller than the molecules of known bodies 

 and which were no other, as we shall see later, than negative electrons 

 free from matter. 



1 Experiment : A bouquet of phosphorescent material rendered luminous by cathode 

 rays. 



