78 Intelligence and Miscellaneous Articles, 



be the object of a fresh study, of which I have today the honour to 

 present to the Academy a rapid summary. 



Conditions of the Experiments. — Without returning to the expe- 

 rimental arrangements indicated in my first Note*, I shall briefly 

 analyze those which have permitted me to extend, and at the 

 same time give a precise account of, my fresh experiments. These 

 are : — the nature, temperature, and pressure of the gas ; the inten- 

 sity, direction, and source of the induced current ; the action of 

 the magnet through the form of its poles, the energy and direction 

 of the magnetization, the distance of the armatures, and the axial 

 or equatorial position of the tube containing the gas f . 



(1) The rarefied gases or substances on which my experiments 

 have been made are hydrogen, nitrogen, oxygen, carbonic acid, car- 

 bonic oxide, bicarburetted hydrogen, sulphur, selenium, iodine, 

 bromine, chlorine, sulphurous acid, fluoride of silicium, bichloride 

 of tin. All of them are far from presenting very pronounced mo- 

 difications, as I shall presently show ; the substances of the chlo- 

 rine group are those most sure to succeed, and produce the most 

 brilliant results. 



(2) Elevation of temperature lessens the effect produced by the 

 magnet. This can be ascertained by causing the induced current 

 to pass for some time within the tube : the heat resulting soon 

 weakens and sometimes renders inactive the magnetic influence. 



(3) The pressure of the gas interferes with the action of the 

 magnet to such a degree that it is possible with the same substance 

 to obtain, according to the conditions, either the sudden cessation 

 of the induced current, or a notable modification in the luminous 

 appearance, or the permanence of the initial tint. 



(4) By varying the intensity of the induced current, effects 

 can be obtained similar to those which result from varying the 

 pressure of the gas : in general, the more feeble the initial in- 

 tensity, the more decided are the magnetic luminous modifications. 



(5) The phenomena are the same when the induced current is 

 derived from a Holtz machine or a Euhmkorff induction-coil. 



(6) Both directions of the induced current, as also of the mag- 

 netization, give pretty nearly identical effects ; certain substances, 

 however, seem to undergo a more energetic influence at the moment 

 of the reversal of the current. 



(7) In the form of the armatures, the surface ought chiefly to be 

 considered ; this should be plane, and such that the capillary tube 

 will be embraced over the greater part of its length. 



(8) It is evident that the more energetic the magnetization, the 

 more pronounced will the phenomena be ; it is usually determined 

 with the aid of a pile of 12-15 Bunsen elements (large pattern). 



(9) Lastly, the action diminishes rapidly with distance ; this is 

 ascertained by gradually removing the tube to about \ centim. from 

 the poles ; beyond that limit the influence of the magnet ceases to 

 be manifest. 



Conclusions. — (1) The first result to be noted is an increase of 



* Comptes Rendus, Nov. 16, 1874, p. 1123. 



t The form of my apparatus has not, up to the present time, enabled m e 

 to compare the effects resulting from these two positions. 



