172 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



which is wound around the pole of the magnet, changes its 

 position in the electro-motive series. 12 A, X., 1874, 97. 



THE VARIABILITY OF SPECTRA. 



The variability of the spectra of glowing gases has lately 

 been studied by Schenck, who finds that this is affected by the 

 following circumstances: viz., by the density of the gas; the 

 strength of the galvanic current that heats it, as w T ell as the 

 method of electric discharge, and the changes of temperature 

 that are produced thereby; the thickness of the glowing stra- 

 tum of gas ; and, finally, the chemical purity of the gas. With 

 regard to the density of the gas, it is found that the diminu- 

 tion of density causes the spectrum to become fainter and 

 fainter, and leads to a change in the relative position of cer- 

 tain of the bright lines, which sometimes will at last become 

 broad bands. When the highest possible degree of rarefac- 

 tion is reached, it is found that the bands respectively be- 

 come groups of well-defined lines that are occasionally 

 merged into each other. 7 C, X., iv., 244. 



THE CONNECTION BETAVEEN SOLAR ECLIPSES AND TERRES- 

 TRIAL MAGNETISM. 



The question as to whether the magnetism of the earth is 

 influenced by a solar eclipse has lately been the subject of a 

 thorough discussion by Denza, who concludes that, from his 

 own and other observations, it follows that the hypotheses 

 and the theories that have been suggested by various per- 

 sons as to the combined influence of the sun and moon on 

 terrestrial magnetism, whether they relate to eclipses or to 

 the ordinary conjunctions of these two celestial bodies, have 

 no value ; and that the connection between these two series 

 of cosmical phenomena is in no wise proved through any ob- 

 servations that have thus far been made. 19 C, 1874,130. 



EARTH CURRENTS. 



A number of valuable contributions to the subject of earth 

 currents have lately been published in the journal of the Lon- 

 don Society of Telegraph Engineers, from which we make a 

 few extracts. It seems that not only are auroras accompa- 

 nied by remarkable electric currents in telegraph lines, which 

 appear to owe their origin to a difference in the electric con- 



