side of the granitic boss in the Orange Free State. It is shown that along its margin the granite has removed, possibly by absorption, but more probably by underhand stoping,' varying amounts of the sediments from point to point; that it has reacted with the basic intrusions in the sedimentary beds, with the consequent production of hybrid rocks; that, in one place, a subsidiary intrusion of granite occurs in the middle of the diabase; and, finally, that the granite, where it comes into contact with the slate members of the Witwatersrand Series, has induced a definite type of metamorphism in them, producing a magnetite-actinolite-staurolite rock, which is of an entirely distinct type from that induced by the basic intrusion associated with the Witwatersrand Beds, a micaceous phyllitic rock. It is suggested that the Vredefort Granite, instead of being Archæan,' is of a post-Pretoria-preKarroo age, if not contemporaneous with, at least connected w the same epoch of igneous activity as the Red Granite' of Northern Transvaal.

6

6

June 10th.-Dr. A. Smith Woodward, F.R.S., President.
in the Chair.

The following communication was read:

"The Ballachulish Fold near the Head of Loch Creran (Argyllshire). By Edward Battersby Bailey, B.A., F.G.S.

The district of Lower Glen Creran has recently been much more carefully examined than heretofore. The course of the Ballachulish Fold had already been determined with approximate accuracy The purpose of the present paper is to draw attention to two phenomena strikingly illustrated by the local evidence :

(1) The complexity of the slides affecting the Ballachulish Core, and the correlated (quite exceptional) occurrence of more groups towards the close of the fold, south-east of the River Creran, than towards the gape, north-west of the same.

(2) The intense secondary refolding of the Ballachulish Fold, and the resultant sinuous outcrop of the Ballachulish Core.

LXXXII. Intelligence and Miscellaneous Articles.

To the Editors of the Philosophical Magazine.

GENTLEMEN,

I wish to indicate an error in the curves of figs. 4 and 5 in "Notes on the Motion of Viscous Liquids in Channels," published in the Philosophical Magazine for July last.

To represent correctly the formula, the gradients should be zero at both ends of the curve of fig. 4 and at the left-hand end of the curve of fig. 5. I am, Yours faithfully, J. PROUDMAN.

The University, Liverpool,

Oct. 8th, 1914.

THE

LONDON, EDINBURGH, AND DUBLIN

PHILOSOPHICAL MAGAZINE

AND

JOURNAL OF
OF SCIENCE.

[SIXTH SERIES.]

DECEMBER 1914.

LXXXIII. The Distribution of the Active Deposit of Actinium in an Electric Field. By A. N. LUCIAN, Ph.D. (Yale)*.

THE

I. Introduction.

HE observation first made by Rutherford, that the active deposit of radium is to a large extent concentracted on the cathode in an electric field, led naturally to the supposition that the deposit consisted of positively charged particles, and that under suitable conditions the concentration could be made complete. The results obtained by Wellisch and Bronsont and by Wellisch‡ separately showed that this supposition is not justifiable. In the second paper cited, it has been shown that the radium deposit atoms consist of neutral and positively charged particles; that even under the most favourable conditions only a definite proportion (about 90 per cent.) of the particles is deposited on the cathode; that there is distinct evidence of columnar or initial as well as volume recombination, and that in general both effects are much more pronounced for the case of deposit particles and gas ions than for the gas ions among themselves.

The work on the actinium active deposit had been quite inconsistent from the beginning, and had given rise to various views in regard to the origin and the sign of the charges

*Communicated by Prof. E. M. Wellisch.

† Wellisch and Branson, Phil. Mag. vol. xxiii., May 1912.

Wellisch, American Journal of Science, vol. xxxvi., Oct. 1913;

Phil. Mag. vol. xxvi., Oct. 1913.

Phil. Mag. S. 6. Vol. 28. No. 168. Dec. 1914.

3 D

carried by the deposit atoms and the mechanism of the transfer in an electric field. Recently, Walmsley published the results of a series of experiments in which he eliminated the disturbing causes existing in the work of previous investigators, such as presence of dust, moisture, &c., and arrived at the following conclusions :-(1) The distribution of the active deposit of actinium between the electrodes is independent of the amount of the emanation, (2) with suitable fields all of the deposit can be collected on the cathode, (3) actinium A and B acquire their positive charge in the process of their creation, (4) in an electric field actinium A and B behave exactly like the positive gas ions produced by their radiations; they recombine in exactly the same way (initial recombination being absent); and the activity on the anode is due entirely to the diffusion of uncharged deposit atoms formed by recombination in the volume of the gas.

The observation that the distribution of activity over a wide range is independent of the amount of emanation and that the activity on the anode is due to the diffusion of neutral particles are in agreement with the results obtained by Wellisch for the case of radium. On the other hand, some of the above results are in direct contradiction to the experimental facts established by Wellisch for the active deposit of radium, which one would expect to hold in the case of actinium also.

The following investigation was undertaken with a view of distinguishing between the two contradictory sets of results and the corresponding theories, based on them, as to the origin of the charges carried by the deposit particles, their mode of transfer and recombination in an electric field, &c. The main objects of the experiments contained in this paper may be briefly summarized as follows:

(1) Is it possible, under suitable conditions, to collect all the active deposit of actinium ou the cathode?

(2) Is columnar as well as volume recombination present? (3) Does volume recombination between the positively charged actinium deposit particles and the negative ions take place at the same rate as the recombination between positive and negative gas ions?

Before describing in detail the experimental procedure, it is not out of place at this stage to draw attention to a funda

*H. P. Walmsley, Phil. Mag. vol. xxvi., Sept. 1913.