1908] on the Carriers of Positive Electricity. 183 



arise in the same way as the negative rays which accompany the 

 Canalstrahlen. Let us consider what happens to the Canalstrahlen 

 as they approach the cathode. When they reach the cathode some 

 of them, as we have seen, get neutrahzed there, some will go further 

 than this, and by gathering another corpuscle will become negatively 

 electrified ; those negatively electrified ones will, however, be repelled 

 from the cathode, and under the action of the electric field will ac- 

 quire a velocity of the same order as that acquired by the positive 

 particles in their approach to the cathode. The rapidly moving- 

 electrified particles will in their course through the gas soon lose 

 corpuscles by collision and thus become positively electrified, forming 

 the positive rays which come from the cathode. Such rays, how- 

 ever, on the view just given start their journey with a negative 

 charge. 



The Canalstrahlen and the positive retrograde rays are not found 

 with all types of discharge ; thus, in the type of discharge sometimes 

 called the flash discharge, whicli occurs 'when a condenser of large 

 capacity is earthed through the discharge-tube, the discharge passes 

 as a column of uniform luminosity stretching from one electrode to 

 the other, and there is no dark space in the neighbourhood of the 

 cathode. In this case I have never been able to detect positive rays 

 of any kind, either in front of or behind the cathode. 



It is important to distinguish between the positive ions to be 

 found in a gas, ionized by Rontgen rays and not exposed to electric 

 fields strong enough to give to them very high velocities ; and the 

 positive ions which, like those in the Canalstrahlen, have very great 

 kinetic energy. For between the positive charges and the molecules 

 there are forces comparable in intensity to those which exist between 

 the atoms of different elements having the greatest chemical affinity 

 for each other. Tims, unless the positive ions possess more than 

 certain amount of kinetic energy, combination will go on with great 

 rapidity and positively charged aggregates will be formed. If, how- 

 ever, the positive ions are moving with great rapidity, they will be in 

 a state analogous to a gas at a very high temperature, and at these 

 very high temperatures chemical combination does not take place. 

 We have seen that the particles in the Canalstrahlen have a velocity 

 of the order of 2 x 10*^ cm. /sec. W^ith a velocity such as this their 

 kinetic energy would be equal to the mean kinetic energy of the 

 molecules of a gas at a temperature of many hundred thousand 

 degrees absolute ; and though, as I have shown,* a positive ion 

 might be expected to combine with a corpuscle if its velocity were 

 but a little less than this, it would not be likely to do so with an 

 uncharged molecule where the attraction would be very much less. 

 If we take the case of a positive ion of mass m projected with a 

 velocity V at right angles to the line joining it with a molecule of 



* Conduction of Electricity through gases, 2nd edit. p. 360. 



