C. GENERAL PHYSICS. 167 



ous gases, sealed up in Geissler tubes, have been experiment- 

 ed upon, the discharge from a Ruhmkorff coil being allowed 

 to traverse the gas. Changes occur in the appearance of the 

 luminous discharge where the magnet is excited ; these 

 changes are accompanied by a change in the resistance of- 

 fered to the current by the gas. Thus a tube containing hy- 

 drogen permitted the passage of a current marking twenty- 

 five decrees on the galvanometer when the magnet was not 

 excited, but when excited the galvanometer reading was forty 

 decrees. It seems to be a law that the augmentation in the 

 intensity of the current is greater with a gas which is a good 

 conductor than with one which is a bad conductor. 12^4, 

 XL, 19. 



NEW SOUKCE OF MAGNETISM. 



M. Donati Tommasi is authority for the statement that if 

 a current of steam at a pressure of from five to six atmos- 

 pheres is passed through a copper tube of two to three mil- 

 limeters in diameter, which is spirally coiled about an iron 

 cylinder, the latter is magnetized so effectually that an iron 

 needle, placed at the distance of some centimeters from the 

 steam magnet, is strongly attracted, and remains magnetic 

 so long as the steam is allowed to pass through the copper 

 spiral. 6 7?, XV., 1875. 



MAGNETIC PERMEABILITY OF IEON, NICKEL, ETC. 



Mr. Rowland, of Troy, New York, in a paper on the mag- 

 netic permeability of nickel and cobalt, states that the views 

 of the English and German philosophers as to the nature of 

 force have given rise to different ways of looking upon mag- 

 netic induction. Thus, the Germans would say that this 

 action was due in part to two causes the attraction of the 

 coil and the magnetism induced in the iron by the coil ; the 

 English, following Faraday, on the other hand, would con- 

 sider the substance in the helix as merely conducting the 

 lines of force, so that no action would be exerted directly on 

 the compass needle by the coil ; but the latter would only 

 affect it in virtue of the lines of force passing along its in- 

 terior, and so there could be no attraction in a perfectly va- 

 cant space. According to the first theory, the magnetization 

 of the iron is represented by the excess of the action of the 



