432 



EVENING DISCOURSE. 



trajeVstories of these electrified particles was a mathematical problem of great difficulty ; 

 but it was solved by Prof. Stormer, who showed that there were certain portions of 

 space, e.g., round the Equator into which the particles could not enter. For example, 

 for a typical case, the forbidden spaces are as shown in Fig. 4. 



Fig. 4. 



Here the forbidden spaces are shown in black and the spaces the electrons can 

 enter shown in white. The earth is supposed to be a very small body situated in the 

 centre of the diagram. You will notice that a toroidal space bounded by electrified 

 particles is supposed to surround the earth, and Prof. Stormer's theory of the origin 

 of echoes of long delay is that the waves constituting the echo have been reflected at 

 the inner surface of this toroid. 



You will perhaps see the matter more clearly in Fig. 5, which shows a quadrant 



StscraoA/ Stream To 



/^OKTHmtff^ AultOftAL ZONE 



A 



Su/ffAC£. 



TOROIOAl. 



Surface 



(iVITH Le^T 

 QUAORANT 

 ffEMOVEO) 



EMRTr Toroidal 

 Space 



£L£CTfKiN Stream to 

 Sour-HERfj Auroral Zone 



Fig. 5. 



of the toroid removed. The maximum distance D depends on the speed of the 

 particles. Thus, for ordinary cathode rays this distance will be about two million 

 kilometres, which would give an echo line of about four seconds. 



It will be seen that Prof. Stormer's theory demands that the waves causing the 

 echo have actually penetrated the Kennelly-Heaviside Layer, and this assumption has 

 been called into question by various writers so that Stormer's theory is not accepted 

 by everyone. 



But it must be admitted that the theory has led to some remarkable predictions. 

 Prof. Stormer states that the months of October and February should be the most 



