Some Lecture Experiments illustrating Syntony. 283 



of the tube. The electric force in the striated part of the 

 discharge is much less than that close to the cathode ; and it 

 might be urged that if such an intense field were required to 

 ionize the gas close to the cathode, the smaller field in the 

 striated discharge would not produce ionization. It must, 

 however, be remembered that the ionization at the cathode 

 has to be produced by positive ions, while that in the rest o£ the ■ 

 field may be due to negative corpuscles ; and it may very well 

 be the case that the large positive ions are less efficient as 

 ionizers than the negative corpuscles. 



XXVI. Some Lecture Experiments illustrating Syntony. 

 By Philip E. Shaw, B.A., B.Sc* 



IN the Journal of the Institution of Electrical Engineers 

 (Feb. 1899'. will be found an account by Prof. Oliver 

 Lodge of his researches in Magnetic Space Telegraphy. 

 The present writer then set up some apparatus to show these 

 methods in a popular lecture. Considerable difficulties soon 

 presented themselves, but success was ultimately attained. 

 Those who are conversant with the above paper will admit 

 that the theory involved in it is of importance, and that any 

 new demonstration of it would be valuable. 



Besides the interest attaching to the theory of syntony, 

 this method of magnetic space-telegraphy has promise of 

 practical and commercial value, and has been shown already 

 by Prof. Lodge to work well over considerable distances. 



The following brief account contains a notice of the general 

 method, of special details introduced by the author, and o£ 

 precautions to be adopted. 



Theory. 

 A summary will be given o£ the more essential points. 



I. The frequency (N) of a circuit of capacity S and self- 

 induction L is 



x/L.S 

 where L is reckoned in henries and S in microfarads. 



II. The mutual induction of two parallel coaxial coils of 

 turns n and m, radii a and b, at distance r apart is, assuming 

 r large, 



y. _ mira? . nirV 1 

 r s 

 * Communicated by the Physical Society : rend March 23, 19G0, 



