296 POPULAR SCIENCE MONTHLY. 



the theoretical consequences deducible from an electric theory of 

 matter. 



I referred above briefly to the origin of radiation, saying that by 

 the method of applying a powerful magnet to a source of light, and 

 examining the minute perturbations in the lines of the spectrum thus 

 produced, it had been proved that the real source of radiation vras an 

 electric charge in rapid orbital motion; and I now go on to say that 

 by careful measurement of the amount of perturbation it has been 

 definitely proved that it is our friends the negative electrons, with a 

 mass about one thousandth of the smallest known atom of matter, that 

 are responsible for the excitation of ether waves or the production of 

 light. Larmor and others have indeed shown mathematically that 

 whenever an electric charge is subject to acceleration, an emission of 

 some amount of radiation is inevitable, by reason of the interaction 

 of its electric and magnetic fields; and it is probable that there is no 

 other source of light or radiation possible except this change in the 

 motion of electrons. It is known, for instance, that the violent accel- 

 eration or retardation of electrons when they encounter an obstacle 

 is responsible for the excitation of Eontgen rays. All light, and all 

 the Hertz waves or pulses employed in wireless telegraphy, are due to 

 electric acceleration, and the greater the rate of change of velocity 

 the more violent is the radiation emitted. 



The charge may oscillate, as in a Hertz vibrator, or it may revolve, 

 as in a source of ordinary light such as a sodium flame. In order to 

 emit perceptible radiation by revolving, it must revolve with extreme 

 speed in a very small orbit, so that its rate of curvature or centripetal 

 acceleration may be considerable; for it is on the square of the value 

 of the average acceleration that the energy of radiation depends. 



9. All this is of the nature of a definite and certain thesis; but 

 now we are going to apply it to our hypothesis that the atom of matter 

 is either wholly or partially composed of electrons in a state of vigor- 

 ous motion among themselves. Such revolving or vibrating electrons 

 are subject to acceleration, either radial or tangential, and must there- 

 fore to a greater or less extent necessarily emit radiation; it becomes 

 natural to inquire whence comes the energy that is radiated away. 



Now in ordinary familiar cases it is the irregular agitation of 

 molecules which we call 'heat' that is being radiated away; and in 

 that case the result is a mere cooling, or diminution of the molecular 

 agitation, which can readily be made up by receipt of similar energy 

 from the enclosures or from surrounding bodies; or, if not made up, 

 it can produce the ordinary well-known effects of 'cold.' But to the 

 motion of the internal parts of an atom the ideas of heat and tempera- 

 ture do not apply. The atom, if it lose energy, must lose what is to 

 it an essential ingredient; and hence this inevitable radiating power 



