On Electromagnetic Waves. 



379 



The chief aim of the author in this research was to fix ap- 

 proximately the temperature at which the rate of loss of 

 permeability begins to be greatest ; and this appears to be 

 300° C, not ouly for the specimen of nickel used by him, but 

 also for that used by Berson, and this, too, both for the tem- 

 porary and total magnetization. The following table shows 

 the rate at which the temporary permeability decreases with 

 rise of temperature between 300° and 320° C. 



Table II. 



Temperature, 



in degrees C, 



t. 



Magnetizing 

 force, 

 M/. 



Permeability, 



Differences between 



values of Mp at 



300° and 320° O. 



divided by 20, 



AMp 



At ' 



» XM/ . 



300 

 320 



| 4-959 { 



141-0 

 966 



I 2-22 



Ill 



300 

 320 



} 11-671 { 



95-5 



73-8 



j 1-08 



12-5 



300 

 320 



} 18183 | 



84-8 

 69-1 



| 0-79 



143 



From this table it is apparent that the rate of decrease of 

 permeability is less the higher the magnetizing force ; so much 

 so indeed that whereas, with a magnetizing force of about 5 

 C.Gr.S. units, there is for each degree rise of temperature a 

 decrease of 11 lines of force per square centimetre ; with a 

 force of 18 the loss of lines per degree is only increased to 14. 



XLIX. On Electromagnetic Waves, especially in relation to the 

 Vorticity of the Impressed Forces ; and the Forced Vibra- 

 tions of Electromagnetic Systems., By Olivek Heaviside. 



[Continued from p. 156.] 



Spherical Electromagnetic Waves. 



15. "T EATING the subject of plane waves, those next in 



-AJ order of simplicity are the spherical. Here, at the 



very beginning, the question presents itself whether there can 



be anything resembling condensational waves ? 



Sir W. Thomson (Baltimore Lectures, as reported by Forbes 

 in 'Nature," 1884) suggested that a conductor charged rapidly 

 alternately + and — would cause condensational waves in 

 the aether. But there is no other way of charging it than by 



