320 Intelligence and Miscellaneous Articles. 



during which the current was closed was long enough to develop 

 the maximum of magnetization. 



Now we see by these numbers that it is when the resistance of 

 the coils is much superior to the exterior resistance that the maxi- 

 mum is attained, and that, for the exterior circuit of 100 kilometres, 

 the maximum is obtained with the helices of 200 kilometres — that is 

 to say, helices presenting double the resistance. Calculation leads 

 to the same deduction ; for in the electromagnet the thickness a of 

 the helix was equal to the diameter c of the electromagnet, and con- 

 sequently the value of H, which must be equal to E to satisfy 



the conditions of a maximum, was found, under the circumstances 

 of my experiments, to be equal to 2H. — Convptes Rendus de VAcad. 

 des Sciences, vol. lxxvi. pp. 368-371. 



STRATIFICATION IN A LIQUID IN OSCILLATORY MOTION. 

 BY J. STEFAN. 



Tine powder diffused in a horizontal tube containing a column of 

 water set in motion to and fro distributes itself in slices or strata 

 perpendicular to the direction of the motion. To. study this, M. 

 Stefan employed a very simple arrangement, which consists in in- 

 troducing water holding in suspension oxide of iron into a horizontal 

 tube of glass with two vertical prolongations. To one of these ver- 

 tical branches is fitted a piece of caoutchouc tubing closed at its 

 free extremity with a cork. By pressing this between the finger 

 and thumb an impulse is communicated to the column of water ; 

 and by repeating the pressure at equal intervals a regular recipro- 

 cating motion is impressed upon it. The powder which has sunk 

 to the lower part of the glass tube is then distributed in streaks 

 which are so much finer and: closer as the motion of the water 

 which carries them with it has less amplitude. 



M. Stefan explains this grouping of the particles by the fact that 

 their displacement is effected more easily in one direction than in 

 the other — which depends either upon the water moving less quickly 

 in one of the two phases of its oscillatory motion than in the other, 

 or else on the shape of the particles. We have here a fact analo- 

 gous to that observed in the production of the lycopodium figures 

 obtained by M. Kundt in acoustic tubes, and having also some 

 affinity to the stratification of the electric fight. At least M. Stefan 

 thinks that this latter phenomenon may be attributed to a cause 

 altogether similar to the one just indicated. " In the Geissler 

 tubes," he says, " a part of the gaseous molecules, playing the same 

 part as the powder-particles in the above experiment, receive from 

 the alternate discharges impulses which are more powerful in one 

 direction than in the other. As to the influence which may be ex- 

 erted by the particular nature of the molecules, it is not necessary 

 to attribute it to their form departing more or less from the sphe- 

 rical ; it is sufficient if we invoke the variety of the motions pro- 

 duced by heat in the different molecules at a given moment." — 

 Archives des Sciences Physiques et JS T aturelles, vol. xlvi. p. 270. 



