240 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 19 2 8 



peiitically, X rays, the ganiiiia rays emitted by radium and the cosmic 

 rays of which we have heard so much recently, are all special cases 

 of electromagnetic waves differing from each other in their essentials 

 only as regards their length. The longest are the wireless waves, 

 which attain lengths of the order of a mile, and the shortest con- 

 stitute the cosmic rays, whose length is comparable with the one- 

 millionth of the one-millionth of the centimeter. 



And then, following Maxwell, once again science made one of 

 those pauses for breath in which many seem to see the end of all 

 that man may hope to know — those dread pauses in which the horizon 

 of discovery seems the boundary thereof. 



Thirty years ago was a time of great depression in physics — a 

 time when would-be Ph. D.'s went about like roaring lions seeking 

 something to measure and finding nothing but the density of a 

 gas or the viscosity of a solid. The sentiment of the times was 

 well voiced by a certain European physicist of eminence who stated 

 that it was probable that all the important experimental discoveries 

 in physics had then been made and that henceforth the investigator 

 must confine himself to a repetition of what had been already done 

 with greater attention to minor matters of precision. 



Even in those days the apparatus cases of most laboratories con- 

 tained curiously shaped glass tubes containing rarefied gases of 

 various kinds which could be made to glow in fantastic manner by 

 sending an electric discharge through them. Few sought to pene- 

 trate the mysteries of those tubes. They would be brought forth on 

 the occasion of popular exhibits in the laboratory, made to go 

 through their alluring performances and then returned to their 

 cases to await the next festivity of the kind. They were not viewed 

 as serious articles of scientific research, but hardly as more than toys. 

 And yet, what a marvelous secret they held ! For it was in one 

 of those tubes that, in 1898, J. J. Thomson discovered one of the 

 two fundamental bricks out of which the universe is built — the elec- 

 tron, the tireless worker whose home is in the atom, whose quivers 

 send us light from the sun, whose ceaseless flight around the atom's 

 center gives the magnet the power to pull, whose motion through the 

 electric cable constitutes the electric current, whose splash when 

 hurled into the atom with great speed is the X ray, whose motions 

 in the antenna send us wireless waves, and whose motions in the 

 radio tube enable us to detect those waves. It is to the electrons 

 that matter owes all its chemical properties. It is electrons from 

 the sun which are responsible for the aurora. The atoms of which 

 matter is composed are so small that about a hundred million of them 

 laid in line would take up but the length of one-third of an inch, 

 but the electron is so small that even in comparison with the atom 

 it is but as a fly compared with a cathedral. It is so light that if 



