338 Mr. G. U. Yule on the Passage of Oscillator 



wave-length one metre. It illustrates the variation in b (the 

 ratio of the transmitted to the incident amplitude at the 

 surface of an infinitely thick slab), when the conductivity and 

 dielectric constant of the slab vary. Curve (1) is drawn for 



Fiar. (5. 



Curves showing the variation in "6" with the dielectric constant and conductivity 

 of the plate, for an undamped wave-train. Wave-length 100 cms. 



20 4U 



Dielectric constant of plate. 

 (1) For a substance of zero conductivity 



(2) 

 (3) 



conductivity -001 X 10 > ft = 1. 



•010X10 



-9 



a non-conducting slab, curve (2) for a slab of conductivity 



•001 x 10 C.G.S. units, and curve (3) for a slab of conduc- 



tivity *01 x 10 or ten times the last. These conductivities 

 are all extremely low, that of a 5 p. c. copper sulphate or zinc 



sulphate solution being roughly *2 x 10 . The curves show 

 very well how rapidly the conductivity of the reflecting plate 

 grows in importance relatively to the dielectric constant even 

 for great wave-lengths. 



But if we take the case of a charge vibrating on an isolated 



perfectly conducting sphere, the amplitude falls to e V§ or 

 about 3 X g of its original value in the time occupied by a com- 

 plete vibration*: this gives us %=54° 41' 8". Let us use 

 this as an example of a damped wave-train to compare with 

 the steady ray, retaining the same wave-length — 1 metre — 

 corresponding to a sphere about a foot in diameter. 



'* J. J. Thomson, ( Recent Researches,' p. 370. 



80 



