282 wien: recent theories of heat and radiation 



One of the phenomena, in which the emission of Ught undoubt- 

 edly takes place thru the collision of molecules and atoms, is 

 the positive rays. There we have atoms and molecules moving 

 with high velocities which can be measured by means of magnetic 

 and electric deflection or by direct methods. One can calculate 

 the mean energy emitted by one atom in one spectral line from the 

 ratio of the emitted intensity in the Doppler line to the number of 

 atoms, which number can be found by observation of the current 

 of positive electricity. On the other hand we find that the par- 

 ticles which are active in the positive rays do not retain their 

 charge but lose it thru collisions with atoms at rest, and after 

 being without charge for a time, they get a new one thru a second 

 collision with a particle at rest. We have therefore always two 

 kinds of particles, one charged and the other uncharged, — neglect- 

 ing the negatively charged particles, whose number is compara- 

 tively small. In the state of equilibrium the number of particles 

 in unit volume losing their charge, is equal to the number receiv- 

 ing a new charge, so that the number of charged as well as of 

 uncharged particles remains constant. But the ratio of the 

 number of charged particles to the number of those uncharged 

 depends upon the number of collisions of both kinds of particles, 

 and is equal to the ratio of the free path of charged particles to 

 the free path of those uncharged. This ratio may be determined 

 by taking away the charged particles in an electric field. 



The free path itself can be found if the charged partic'es are 

 deflected and the distance measured, thru which the uncharged 

 particles must pass before a definite number receive their positive 

 charges. It is found that the free path of the uncharged particles 

 is greater than that of the charged particles but that the ratio of 

 the one to the other depends on the pressure of the gas at rest. 

 This is not in accord with the fundamental concept of the kinetic 

 theory of gases, which demands that the free path be inversely 

 proportional to the pressure. Also the absolute value of the free 

 paths is not inversely proportional to the pressure but at low pres- 

 sures diminishes more slowly than the pressure increases. These 

 results show that the atoms cannot be regarded as entirely inde- 

 pendent of each other. One may also observe that the absorption 



