Intelligence and Miscellaneous Articles. 151 



INTERFERENCE EXPERIMENT WITH ELECTRICAL WAVES. 

 BY PROF. VON LANG. 



The experiment described corresponds to the well-known acous- 

 tical one of Quincke. The electrical wave from a Eighi's exciter 

 is divided into two parts with unequally long paths ; after joining, 

 the partial waves interfere, which is demonstrated by a Branly's 

 Coherer. If the one wave is successively lengthened, both waves 

 will be alternately strengthened and weakened, and as many as 

 four maxima and minima can be easily shown. The experiments 

 were made with tubes of nearly 60 millim. diameter. Tubes with 

 half that diameter did not show the phenomenon. If in one of 

 the two tubes a paraffin cylinder is introduced which entirely fills 

 it, the position of the maxima and minima is displaced, from which 

 the refractive index of paraffin can be calculated. The author 

 found for it 1-65-1-70. Similar experiments with sulphur gave 

 for its refractive index 2-33-2-37. These numbers are considerably 

 higher than the values found by Righi, which were, for paraffin 

 1*43 ; for sulphur 1-87. The length of the electrical waves in 

 these experiments was 80 millim., the diameter of the knobs of the 

 exciter 106 millim. — Wiener Berichte, Oct. 24, 1895. 



ON ELECTRIFIED ATOMS. 



To the Editors of the Philosophical Magazine. 

 Gentlemen, 



I find that the view expressed by me in my paper " On the 

 Eelation between the Atom and its Charge" (Phil. Mag. Dec. 1895, 

 p. 541), that a negatively electrified atom moved more rapidly than 

 a positively electrified one in the same electric field, was arrived at 

 from different reasons by Professor Schuster, and given by him 

 more than five years ago in the Bakerian Lecture for 1890. I am 

 glad to find that this view is held by so eminent an authority, and 

 regret that I had previously overlooked such strong evidence in its 

 favour. There is another result given in the same Bakerian 

 Lecture which I ought to have quoted. I allude to Mr. Stanton's 

 interesting experiments on the escape of electricity from a hot 

 copper rod surrounded in one case by oxygen and in another by 

 hydrogen. 



I am, Gentlemen, 



Tours very sincerely, 

 Cavendish Laboratory, Cambridge, J. J. THOMSON. 



January 20, 1896. 



