Intelligence and Miscellaneous Articles. 149 



attributed to the sudden intrusion of oceanic waters into an area 

 below sea-level. 



The author then pointed to the traces of terrestrial vegetation in 

 the Lower Greensand as evidence of the continuance of river- action 

 after the close of the AYealden jDeriod. 



In the concluding portion of his paper the author rcfered to the 

 relation of the Punfield beds of Mr. Judd to the Neocomian and 

 AVealden strata of the south-east of England. From the sequence 

 of the strata, no less than on palseontological evidence, he considered 

 the whole of the so-called " Punfield formation " of the Isle of Pur- 

 beck to be referable to the Lower Greensand of the Atherfield 

 section. 



XX. Intelligence and Miscellaneous AyHicles. 



RESEARCHES ON THE ELECTRIC JET IN RAREFIED GASES_, AND IN 

 PARTICULAR ON ITS MECHANICAL FORCE. BY MM. A. DE LA 

 RIVE AND E. SARRASIN. 



ONE of us has already occupied himself with the phenomenon of 

 the rotation experienced, under the magnetic influence, by the 

 electrical jet produced, by means of the RuhrakorfFcoil, in a rare- 

 fied gas. We have just resumed the experimental study of this pheno- 

 menon, in order to effect a better determination of its nature and its 

 conditions. 



In this extract we limit ourselves to a statement of only a few of 

 the results we have obtained, reserving the details of the experi- 

 ments, and the description of the apparatus, for the memoir which 

 is about to be printed. 



In a first series of experiments we sought to determine the influ- 

 ence of the degree of rarefaction of the gas, and of its nature, on 

 the velocity of rotation of the jet. For this purpose we placed on 

 each of the poles of a powerful electromagnet a cylindrical glass jar, 

 in which the electric jet, passing from a knob in the centre to a ring, 

 could, under the magnetic influence, turn in a horizontal plane like 

 the hand of a watch. The two jars were perfectly similar; the 

 magnetic force of the two poles on which they rested was exactly 

 the same ; and the same current traversed successively the rarefied 

 gas in the two jars arranged one after the other in the circuit. The 

 result was that when the two gaseous media were identical, the ve- 

 locity of rotation of the jets was the same in both jars ; this we 

 verified by numerous experiments. That velocity, then, could only 

 vary with the condition or the nature of the gaseous media, since 

 all the other circumstances were unchanged. 



Thus, with atmospheric air, the number of turns of the jet in 30 

 seconds, at 13 millims. pressure, was 105, alike in both jars ; now, 

 the air in one of the jars being kept at 13 millims. jDressure while 

 the pressure was increased to 26 millims. in the other, we had only 

 63 turns in the latter, but 102 turns in the former; and at 39 mil- 

 lims. pressure the number of turns was only 54, while it was dQ in 



