ELECTRIC OSCILLATIONS AND ELECTRIC WAVES. 245 



millimeter and it should be filled with the rare gas neon at a 

 pressure of 2 or 3 millimeters of mercury. 



The open end BB' of the "transmission line" in Fig. 185 is a 

 voltage antinode, and usually a number of voltage nodes are 

 found by moving the vacuum tube T along. It is interesting 

 to note in this connection that the frequency of the oscillations 



Fig. 186. 



of the system CrgrD may be found by measuring the distance 

 between adjacent voltage nodes on the "transmission line" 

 ABA'B', remembering that this is the distance travelled by an 

 electromagnetic wave during one-half of a complete oscillation. 

 Thus, if the distance between adjacent voltage nodes is 3 feet 

 the total wave length is 6 feet, and the period of one oscillation 

 is the time required for an electromagnetic wave to travel over 

 this distance, namely 6.1 X io~ 9 of a second, which corresponds 

 to a frequency of 320,000,000 oscillations per second. 



ELECTROMAGNETIC ACTION. 



129. Mechanical conceptions of magnetic and electric fields.* 

 It is of the greatest help towards the clear understanding of 

 electric and magnetic phenomena to obtain clear mechanical 



* Sir Oliver Lodge's Modern Views of Electricity is perhaps the best elementary 

 treatise on this subject. 



The most complete mechanical conception of the electromagnetic field is that 

 which is based upon Lord Kelvin's gyrostatic model of the ether. This gyrostatic 

 model of the ether is a mechanical structure which is capable of reproducing most 

 of the known phenomena of electricity and magnetism and of light. See Aether 

 and Matter, by Joseph Larmor, Appendix E, Cambridge, 1900. Lord Kelvin's 

 gyrostatic model of the ether has led to a hydrodynamic conception of the ether, 

 due chiefly to Larmor, in which the ether is assumed to be a perfect fluid endowed 

 with the necessary elastic properties by an indefinitely fine-grained whirling motion. 

 On the basis of Lord Kelvin's gyrostatic conception of the ether and also on the 

 basis of Larmor's turbulent ether, the magnetic field is thought to consist of a 

 simple flow of ether along the lines of force of the magnetic field. This conception 

 of the magnetic field is very different from the conception (Maxwell's) which is 

 outlined in this text. 



