144 Rutherford: Modern 



Zeeman, who observed that the bright lines of the spec- 

 trum were displaced and broken up into a number of 

 separate lines by exposing the source of light in a strong 

 magnetic field. The full significance of the " Zeeman 

 efifect " will be discussed a little later. 



In this development, theory was distinctly in advance 

 of experiment, and we shall now go back for a moment 

 and trace the gradual development of a new line of 

 attack which has yielded results that, in the last ten 

 years, have profoundly modified and extended our con- 

 ceptions of electricity and matter. 



It had early been recognized that there were distinct 

 differences in the discharge of positive and negative elec- 

 tricity. A sharp point, for example, discharges negative 

 more readily than positive electricity, while the appear- 

 ance of the spark is different at the two discharging ter- 

 minals. This difference in appearance of the discharge 

 is still further accentuated when a discharge is passed 

 through a rarified gas. Anyone who has witnessed the 

 beautiful and varied luminous effects produced when 

 an electric discharge is passed through a vacuum tube, 

 cannot fail to have been impressed by the remarkable 

 differences in the distribution of luminosity at the two 

 electrodes. This dissymmetry in the discharge appeared 

 at first to indicate that there existed a profound and 

 radical difference between the behavior of positive and 

 negative electricity, but we shall see later that these dif- 



