Intelligence and Miscellaneous Articles. 83 



from lengthening, it shortens ; instead of decreasing, its resistance 

 to rupture and the intensity augment ; and the light gently re- 

 descends to resume and keep its place at the extremity of the car- 

 bons. If, on the contrary, the current should increase, the arc 

 bends and becomes concave towards the carbons ; but, its tendency 

 to ascend counterbalancing the action of the directing current, it 

 never stretches enough to break. The best economic conditions 

 are attained when this curve is just pronounced enough to prevent 

 the ascensional movement of the light. In this case the unavoid- 

 able noise of the electric light is reduced to its minimum, because 

 the amplitudes of the vibratory motion are the smallest possible. 



In brief, the burner which I submit to the Academy, with its 

 points beneath, realizes considerable advantages: — (1) that of sim- 

 plicity, since it needs no mechanism and requires no preliminary 

 preparation ; the whole amounts to a support and some carbons ; 

 (2) that of mechanical economy, since the number of the flames is 

 almost doubled ; (3) increase of light, since each of the new foci 

 is nearly twice as effective as the old ones ; (4) the quality of the 

 light, which is whiter ; (5) a more advantageous disposition of the 

 foci, which direct their greatest sum of light downwards, where it 

 is of use, instead of losing it skywards, where it would be useless ; 

 (6) lastly, economy of the combustible, since in proportion to the 

 size of the carbons the consumption is less. All this constitutes 

 for the electric light a sensible advance, and cannot fail to enlarge 

 the place it has already taken in public lighting, thanks to the 

 improvement of the engines, to the carbons of M. Carre, and to M. 

 Jabloschkoff's candle. — Comptes Hendus de V Academie des Sciences, 

 April 28, 1879, t. lxxxviii. pp. 829-832. 



ON THE DEVIATIONS OF AMPERE S THEORY OF MAGNETISM FROM 



THE THEORY OF THE ELECTROMAGNETIC FORCES. BY J. 



STEFAN. 



The divergences between the two theories stand out most clearly 

 when the moments with which a current-element tends to rotate 

 an elementary magnet are determined according to both. Accord- 

 ing to the electromagnetic theory, the current-element rotates the 

 magnet out of the plane when both stand perpendicular to the line 

 joining them and are situated in the same plane ; while according 

 to Ampere it cannot act at all upon the elementary current equiva- 

 lent to the magnet, since it stands perpendicular to every part of the 

 latter and at the same time to the connecting lines leading to them. 



If the current-element falls into the connecting line, according 

 to the electromagnetic theory it exerts no rotating action upon the 

 magnet ; but according to Ampere it sets the equivalent elementary 

 current continuously rotating about its axis — an action which is 

 quite foreign to the electromagnetic theory. 



If the magnet lies in the direction of line of conjunction, a cur- 

 rent-element perpendicular to this, according to both theories, 

 rotates the magnet out of the plane, but according to Ampere's 

 theory with a moment tAvice as great as according to the electro- 

 magnetic. 



