312 Intelligence and Miscellaneous Articles. 



tensity. It seems, therefore, well established that a gas, although 

 possessing several spectral lines, may manifest itself in the spec- 

 troscope by the presence of a single line, the others remaining invi- 

 sible on account of the want of brightness of the luminous body. 

 There is, then, a great probability that a known element exists in 

 a celestial body when a line belonging to that element has been 

 proved to exist in the spectrum. And as the spectra of the nebulae 

 37 HIV. &c. show those lines of nitrogen and hydrogen which 

 longest resist extinction, we may, with Huggins, regard those 

 nebulae as including nitrogen and hydrogen among their constituent 

 substances, and attribute the relative invisibility of the other lines 

 to absorption by space, acting equally upon rays of every degree of 

 refrangibility. We say " relative invisibility," because it is probable 

 that the lines now invisible could be perceived with more powerful 

 telescopes than those which we possess at present. — Ball. Soc. cle 

 VAcad. royale de Belgique, ser. 2, t. Ixix. no. 2, 1880. 



ON THE ELECTROMOTIVE FORCES WHICH APPEAR IN FREE JETS 

 OF WATER, 



We have been favoured by the author, M. J. Elster, with a copy 

 of his Inaugural Dissertation* on the above subject, which appears 

 to have been prepared under the guidance of Prof. Quincke. It 

 is considered as proved by these investigations : — 



1. That if an electromotive force is to arise in a free jet of water, 

 it is necessary that the water particles be in contact with a solid body ; 



2. That the evolution of electricity takes place only where the 

 particles of the liquid undergo friction, so that only a relatively 

 small portion of the water-jet contributes any thing to the deve- 

 lopment of electricity ; 



3. That when the velocity of a jet issuing constantly from the 

 same orifice is varied, the electromotive forces are proportional to 

 the vires vivce of the liquid particles — a relation the reason of which 

 is found in the law of the conservation of energy ; 



4. And, lastly, that the electromotive force is dependent on th e 

 nature of the body which is in contact with the liquid. 



From these results the author draws the following conclusions : — 



1. The motion of a fluid does not by itself produce any electro- 

 motive force. Consequently the inference deduced by Edlund from 

 his unitary theory of electricity has not been confirmed. 



2. Capillary electric currents are conditioned solely by the fric- 

 tion of the particles of the fluid in motion — in nonhumectant fluids 

 by their friction against the particles of the solid wall, in humec- 

 tant fluids by friction on the particles of a layer of the same fluid 

 condensed upon the surface of the solid body, which behaves towards 

 the less dense layer like a heterogeneous substance. 



3. The capillary-electric currents discovered by Quincke are 

 identical with the friction-currents, first observed by Zollner, which 

 make their appearance in the rubber of an electrical machine. 



* Ueber die in freien Wasserstrahlen auftretenden electromotor -is chen 

 Kriifte. Von Julius Elster. Leipzig, 1879. 8vo ; pp. 40 and 1 plate. 



