184 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1914. 
ing savants were triumphantly determining the effective radius as 
about 1078 em. (a convenient shorthand for the hundred millionth 
of a centimeter). 
The discovery of electrons as the cathode rays of an electric dis- 
charge in an exhausted tube, and as the beta rays of radium, opened 
up new regions. It appears that negative electricity consists of 
electrons with their accompanying but unexplained effects in the 
ether. Electrons in motion produce magnetic fields. Their effec- 
tive mass is about one eighteen hundredth part of that of a hydrogen 
atom, and their effective radius one hundred thousandth. The 
greatest known speed of electrons nearly approaches that of light. 
The Zeeman. effect, or separation of a single line in the spectrum 
by suitable magnetic fields into two or more lines, proved con- 
clusively that the vibrations of negative electrons in the atom are 
the cause of the disturbances in the ether which we know as light. 
4. The first scheme of an electronic atom, propounded by Sir 
Joseph Thomson, was a sphere of positive electricity of undefined 
character, within which revolved concentric rings of electrons in the 
same plane. There necessarily followed the simplicity of circular 
motion under a force to the center, proportional to the distance be- 
tween the electron and the center of the atom. ‘ 
5. Previous to this Lord Rayleigh had called attention to a serious 
anomaly. In a train of waves of a periodic character, the electric 
intensity E varies as the sine of nt, where ¢ is the time and 2z/n is 
the period. As the equations involve the second differential of EK, 
it appears inevitable that the square of n should appear in the law 
for spectral series. As a matter of fact there appears not the square 
of n, but n itself. It is desirable to be more explicit. If parallel 
light from a luminous source passes through a slit and a prism, 
together with suitable lenses, then the eye or photographic plate can 
detect a number of bright lines forming the spectral images of the 
slit for different colors, provided that the light is from luminous 
mercury vapor or hydrogen, or some such source. Many of these 
lines have been found to belong to one or more series crowding to- 
gether toward the violet end. Balmer and Rydberg have found 
that the general type of formula for their frequency n is 
ee | 
n=Ni(Ge— ps} 
where N, is a universal constant called Rydberg’s number, the same 
in value for all electrons of all atoms; and @ and 6 are whole numbers 
or integers. We shall refer later to the importance of Rydberg’s 
constant and of this magnificent generalization. 
