6 Chant — Experimental Investigation into the 



trolytically on the surface of a metal forming a resonator a 

 shell of another metal, he determined what thickness he must 

 add in order that the resonator should behave as though 

 formed of the second metal. He used an electrometer method, 

 and his results are shown in the following table : 



Table II. 



Original Final Thickness 



Reading. Reading. of Layer. 



Copper on iron 13*4 105 0*012 mm 



Zinc on iron 13*4 11 0'016 " 



Zinc on copper 100 80 0*012" 



Nickel on copper 100 40 0-010" 



Cobalt on copper 100 10 0-003" 



Iron on copper 100 10 0*003" 



The wave-length used by Bjerknes was 420 cms and the fre- 

 quency, therefore, about 70 millions per second. 



I have not been able to find any record of experiments on 

 the thickness of the effective portion of the metal of an oscil- 

 lator except by Preece and Righi. 



Tho former, in describing experiments made in conjunction 

 with Marconi on signaling without wires, says : * 



" The distance at which effects are produced with such rapid 

 oscillations depends chiefly on the energy of the discharge that 

 passes. A six-inch-spark coil sufficed through 1, 2, 3, up to 

 four miles, but for greater distances we have used a more 

 powerful one — one emitting sparks 20 inches long. It may 

 be pointed out that this distance increases with the diameter 

 of the spheres and it is nearly doubled by making the spheres 

 solid instead of hollow." 



He used the regular Righi oscillator with 10 cm spheres 

 sparking in vaseline oil, from which, he says, there were 

 emitted waves 120 cms in length, with a frequency of 250,000,- 

 000 per second. How this wave-length was determined is not 

 given. 



Righi states :f 



" Finally I made the perhaps unlooked-for observation that 

 an oscillator composed of hollow spheres is less effective than 

 one such of massive spheres. For example, when the oscilla- 

 tor had massive spheres of about 4 cms diameter, the action on a 

 resonator first ceased at about 11 meters ; while, on the other 

 hand, it ceased at about six meters when these spheres were 

 replaced by hollow ones of equal external diameter and about 

 l-5 mm of wall-thickness. Two others with yet decidedly thin- 



*Proc. Royal Inst., vol. xv, p. 472 (1897). 



f Righi, Optik der elektrischen Schwingungen, pp. 14, 15. 



