Intelligence and Miscellaneous Articles. 387 



2. This principle holds also if the magnetic field does not 

 exceed 1*2. 



3. If the magnetic field is stronger, then the first coefficient 

 of enfeeblement which is due to the current on opening, first of 

 all exceeds the following ones obtained in the same way by but 

 little, but afterwards by 5 or 6 per cent., if the magnetic field is 

 3 or 4. Hence in order to obtain a stable value for the strength- 

 ening and the enfeeblement with these high values, a bar magnet 

 should first of all be subjected to the same strengthenings and 

 enfeeblements. 



4. With powerful magnetic fields the first closing of the current, 

 if this strengthens the magnetic moment of the bar, has a greater 

 constant than the following ones ; but it does not attain the 

 magnitude of the constant of enfeeblement produced by the mag- 

 netic field on closing. 



5. Magnetizing forces, even when they are ten to twelve times 

 as much as the earth's magnetism, produced no considerable 

 durable changes of the permanent state. Forces which were 

 twenty times as strong as the horizontal intensity produced un- 

 doubted changes in the moment of the bar. — Wiedemann's Annalen, 

 No. 9, 1886. 



ON THE ELECTRICAL CONDUCTIVITY OF GASES AND VAPOURS. 

 BY M. JEAN LUVINI. 



It follows from the experiments of Becquerel, Grove, Matteucci, 

 Marangoni, Agostini, and others, that gases and vapours are very 

 bad conductors of electricity. Grove demonstrated this proposition 

 for air at very high pressures ; Becquerel and Matteucci for very 

 low pressures (1 to 3 millim.). MM. Mascart and Joubert place air 

 and vapours and generally all gases in the class of bad conductors ; 

 and Sir W. Thomson has stated that aqueous vapour is an excellent 

 insulator. 



Notwithstanding this we still read in treatises on Physics, and 

 it is repeated in lectures, that moist air and vapours conduct 

 electricity ; and this very serious error is the base of several 

 theories. 



I have made several sets of experiments on this subject, the 

 results of which, combined with those of other experimenters, have 

 led me to conclude that gases and vapours, whatever be the pressure 

 and temperatures, are perfect insulators, and cannot be electrified 

 either by friction with each other or with solids or liquids. 



I arrange the experiment so that the fluids in which the electri- 

 fied bodies are introduced cannot be deposited as liquid on the 

 whole length of the insulating supports. In a large room a long 

 thread consisting of seven cocoon fibres, without torsion and 

 without joints, is stretched. In its centre is suspended a hollow 



