Intelligence and Miscellaneous Articles. 473 



kathode, we have a broad space filled by molecules which are not in 

 collision with each other. Only when the molecules come into col- 

 lision with each other beyond this space do they become luminous, 

 so that the space surrounding the kathode is non-luminous. Obser- 

 vation, however, shows that this space is not non-luminous, but 

 emits light of a deep blue colour, to produce which the extremely 

 small quantity of gas present must possess a high emissive power. 

 Moreover, immediately surrounding the kathode there exists, as 

 already noted, the first layer of a bright yellow colour. Further, 

 Dr. Goldstein observes that molecules thus driven on from the 

 kathode could only in special cases pursue a rectilinear path, since 

 it is clear that a molecule charged with electricity, which enters 

 into motion in consequence of its presence in an electric field, must 

 describe a line of force. If the surface of the kathode were sphe- 

 rical, such lines of force would, it is true, be straight: but in the 

 usual case, when the kathode consists of a straight thin wire, the 

 lines of force would be hyperbolas whose foci would be the ends 

 of the wire. The shadow of a straight wire placed near to and 

 parallel to a straight kathode of slightly greater length would 

 therefore considerably exceed the wire itself in length. Obser- 

 vation shows, however, that the shadow is almost exactly of the 

 same length as the wire itself, and that the rays are actually rec- 

 tilinear and at right angles to the kathode. 



As already stated, Dr. Goldstein rejects all three theories, as 

 insufficient to afford full explanation of the facts. 



"Williamson's Integral Calculus. 

 To the Editors of the Philosophical Magazine and Journal 

 Gentlemen, 

 In the flattering reference to my investigations in kinematics 

 contained in your review of Williamson's ' Integral Calculus ' in 

 the April number, there is one misapprehension that I feel bound 

 to remove. The results obtained by Messrs. Leudesdorf and Kempe 

 are spoken of as suggested by my earliest one. They were, how- 

 ever, quite independently arrived at ; indeed in publication, though 

 not, I think, in composition, Mr. Leudesdorf s theorem had the 

 priority of mine by two months. 



I am, Gentlemen, 



Yours faithfully, 

 Queen's College, Oxford, May 11. E. B. Eeeiott. 



LXIII. Intelligence and Miscellaneous Articles. 



NOTE BY MR. JR. SHIDA ON HIS ARTICLE (PHIL. MAG. DEC. 1880), 

 " ON THE NUMBER OF ELECTROSTATIC UNITS IN THE ELEC- 

 TROMAGNETIC UNIT*. 



fXS page 360, Phil. Mag. for May 1881, Dr. C. E. A. Wright has 

 v ' made the following statement :— " That the E.M.E. of a Daniell 

 cell is somewhat less when generating a current than when no cur- 

 rent passes has already been shown to be the case by Waltenhofen 

 * Communicated by Sir William Thomson. 



