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of shape, indicating that the spark-length varies with the current in different ways for different materials so that the material which gives the longest spark with a particular current does not necessarily give the longest spark with another current. Thus with a current of 15 amperes the spark is longest with carbon poles, shortest with platinum ones; but, on reducing the current to 3 amperes, the easily fusible metals bismuth and lead give the longest sparks.

Perhaps the most interesting point brought out, however, is in connexion with the behaviour of the different materials on reversal of the current. With the metals iron, copper, tin, nickel, zinc, and with carbon, reversing the current produces no perceptible difference in the spark-length; but with lead, platinum, and aluminium poles the spark-length for the larger currents is notably greater when the fixed pole is negative than when it is positive.

Owens College, Manchester.

LXIII. Notices respecting New Books.

Production et emploie des Courants alternatifs. Par L. BARBILLION. Paris: G. Carré et C. Naud, 1901. ("Scientia " Series, No. 11.) Pp. 103.

WE E have already had occasion to review briefly some of the volumes belonging to the "Scientia" series, which is being brought out by the well-known French publishing firm, Messrs. G. Carré et C. Naud. The present volume of 103 pages contains a digest of alternating-current theory. The title of the book is misleading, and it seems to us that "the theory of alternating currents" would have been a much truer indication of the contents of the book than the title selected by the author. The brief discussion of continuous-current machines given on pp. 8-14 seems entirely out of place, and is, of course, very incomplete. On p. 8 we have a diagram (fig. 2) of the magnetic field in a two-pole dynamo which would be excusable in a pre-historic treatise on the subject, but which it is surprising to find in an up-to-date book; no attempt is made to show the true course of the lines and their refraction as they pass from iron to air or vice versa. Taken as a whole, however, the book is a useful and concise exposition of the principles underlying the applications of alternating currents, and contains a good account of several interesting developments of recent date.

LXIV. Proceedings of Learned Societies.


[Continued from p. 580.]

June 19th, 1901.-J. J. H. Teall, Esq., M.A., V.P.R.S.,
President, in the Chair.

HE following communications were read :



1. On the Use of a Geological Datum.' By Beeby Thompson, Esq., F.G.S., F.C.S.

A proper interpretation of geological phenomena frequently requires that allowance shall be made for differential earthmovements that have taken place since the period under consideration. Present differences of level in rocks of the same age may be due to actual differences in depth of the sea-floor on which they were deposited; but they may also be the result of subsequent differential earth-movements. The rock selected as a datum should combine as far as possible the following characteristics :-It should be thin, of considerable horizontal extension, having similarity in physical characters and paleontological contents over a large area, and situated as near as possible, in vertical sequence, to the reference

deposit. In Northamptonshire three formations meet these requirements-the Rhætic Beds, the Marlstone Rock-bed, and the Cornbrash. The author applies the Marlstone Rock-bed as a datum to the study of the five chief deep explorations in Northamptonshire, with the following results :-While the old land-surface (below the Trias) now varies in height by more than 250 feet, the variation in thickness of the rocks between it and the Middle Lias only reaches 56 feet; and although the old land-surface is actually lowest where the Rhætic rocks have not been detected, when compared with the position of the Marlstone it is found to be the highest. The further application of the same method enables the author to recognize Rhætic rocks at Northampton, to correct the record of the Kingsthorpe shaft, and to explain the presence of Triassic saline water in the Marlstone. A revised section of the Kingsthorpe shaft is given. Another point proved is that a general levelling-up process was going on just before the beginning of the Lower Liassic Period, and another at the close of the Middle Liassic Period.

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2. 'On Intrusive, Tuff-like, Igneous Rocks and Breccias in Ireland.' By James R. Kilroe, Esq., & Alexander McHenry, Esq., M.R.I.A. Many fragmental igneous rocks, although resembling tuffs, cannot be regarded as ejectamenta on account of their character and mode of occurrence in the field. Rocks of this type occur to the east of Lough Eake in Donegal, in the district of Forkhill in Armagh, at Blackball Head in Cork, in Waterford, near Arklow, in Wexford, and elsewhere. Sometimes they consist of partly fused and broken-up felspathic mica-schist merging into felsitedykes, at other times of brecciated slate, granite, and felsites embedded in a scanty andesitic matrix. At Blackball Head, the rocks cross the bedding of the associated sedimentary rocks of the region. The authors agree with Prof. Lapworth in considering it possible that igneous matter making its way between the moving masses may consolidate as sills when the pressure is great..... As movement progressed intermittently, we should have the formation of subterranean agglomerates, tuffs, and breccias, which would be forced sometimes between bedding-planes, sometimes into dykelike fissures.' A series of sections is exhibited to illustrate how tuff-like masses invade black slate of Llandeilo age in the South-east of Ireland, generally adhering to the direction of bedding, but frequently cutting across it and detaching numerous pieces from the slate, which are more abundant near the margins of the intrusion than elsewhere. The masses frequently assume a tuff-like appearance. At Arklow Rock tongues of tuff-like rock penetrating black slate of Llandeilo age contain pieces of Limestone of Bala age, as well as pieces of the slate. The development of vesicular texture in lapilli-like, contained, fragments may be due to the simple release of pressure.


ACOUSTICAL notes, 280.

Adams (E. P.) on the electromag-
netic effects of moving charged
spheres, 285.

Ether and gravitational matter
through infinite space, 161.
Air, on the ionization of, by phos-
phorus, 477.

Amagat (E. H.) on the isothermals
of fluids, 651.

Appleyard (R.) on a direct-reading
conductivity-bridge, 178.
Archibald (E. H.), a study of grow-
ing crystals by instantaneous
photomicrography, 488.

Ashton (A. W.) on a model which
imitates the behaviour of dielec-
trics, 228; on the electrification
of dielectrics by mechanical means,
233; on the resistance of dielec-
trics and the effect of an alterna-
ting electromotive force on the
insulating properties of india-
rubber, 501.

Atom, on the electrical structure of
an, 425.

Balmer's formula, kinematical analy-
sis of, 253.

Baly (E. C. C.) on the spectrum of
cyanogen, 386.

Barrow (G.) on the occurrence of
Silurian rocks in Forfarshire and
Kincardineshire, 578.

Barus (Prof. C.) on the absorption
of ionized phosphorus emanation
in tubes, 40; on the transmission
of the emanations of phosphorus
through air and other media, 391;
on the simultaneous volumetric
and electric graduation of the
steam-tube with a phosphorus
ionizer, 477.

Phil. May. S. 6. Vol. 2. No. 12.

Beats, notes on, 283.

Beattie (R.) on the length of the
break-spark in an inductive
circuit, 653.

Bismuth, on the electrical resistance
of, 300 on the thermomagnetic
and thermoelectric properties of
crystalline, 325.
Boltzmann-Maxwell doctrine, notes
on the, 10, 241, 403.
Books, new: -Ewing's Magnetic
Induction in Iron and other
Metals, 150; La Rivista Tecnica
delle Scienze, delle Arti applicate
all' Industria e dell' Insegnamento
Industriale, 151; Osborne Rey-
nolds' Papers on Mechanical and
Physical Subjects, 241; Poincaré's
Electricité et Optique, 243; Born-
stein's Leitfaden der Wetterkunde,
244; Rapports présentés au Con-
grès International de Physique,
320; Hamilton's Elements of
Quaternions, 418; Williamson
and Tarleton's Elementary Trea-
tise on Dynamics, 574; Classen's
Ausgewählte Methoden der ana-
lytischen Chemie, 575; Vogt's
Entstehen und Vergehen der Welt
als kosmischer Kreisprozess, 576;
Barbillion's Production et Emploi
des Courants alternatifs, 659.
Bromwich (T. J. I A.) on the poten-

tial of a symmetrical system, 237.
Brooks (H.) on the damping of
oscillations in the discharge of a
leyden-jar, 92.

Buchanan (Dr. J.) on magnetic
induction in iron and other metals,

Bullen (Rev. R. A.) on two well-
sections, 321.
Dec. 1901.

2 X

Burbury (S. H.) on Boltzmann's law
of distribution and van der Waals'
theorem, 403.

Chree (Dr. C.), applications of elastic
solids to metrology, 532, 594.
Conductivity-bridge, on a direct-
reading, 178.

Convection, on the magnetic effect
of electric, 144, 179, 235, 285,

Coomara-Swámy (A. K.) on the
occurrence of corundum at Pont-
Paul, 153.

Crémieu (Dr. V.) on the magnetic

effect of electric convection, 235.
Crystallization, on the velocity of,


Crystals, on rotatory polarization in
biaxial, 361; study of growing, by
instantaneous photomicrography,


Current, on the dependence of the,
through conducting gases on the
direction of the electric field,


Cyanin, on the anomalous dispersion
of, 317.

Cyanogen, on the spectrum of, 386.
Dielectric strain, on, 527.
Dielectrics, on a mcdel which
imitates the behaviour of, 228:
on the electrification of, by
mechanical means, 233; on the
resistance of, 501.
Discharge of a leyden-jar, on the
damping of the oscillations in
the, 92; on the spark-, 311.
Distribution, on Boltzmann's law of,

Double-refraction in moving viscous
liquids, on, 469; on accidental, in
liquids, 524.

Elastic solids, applications of, to
metrology, 532, 594.

Eletric convection, on the magnetic
effect of, 144, 179, 235, 285, 319.

field, on the dependence of the
curent through conducting gases
on the direction of the, 210.


resistance of bismuth, on the,

Electrodes, on the drop of potential
at the, in vacuum-tube discharge,


Electromagnetic effects of moving
charged spheres, on the, 285.

Emission-function, on the complete,
379, 573.

Energy, on the partition of, 416.
Equilibrium, on the velocity of re-
action before complete, 50.

Fit, on lines and planes of closest,


Fleming (Dr. J. A.) on a model
which imitates the behaviour of
dielectrics, 228.

Fluids, on the isothermals of, 651.
Fraser (W. G.) on the breaking of
waves, 356.
Freezing-point of water,

on the
absolute value of the, 135.
Gases, on the dependence of the
current through conducting, on
the direction of the electric field,
210; on the ratio of specific heats
in, 241, 638; on the radiation
from, 422.
Geological datum, on the use of a,


Geological Society, proceedings of
the, 151, 321, 577, 659.
Gibson (W.) on the coal-measures
of Staffordshire, 158.

Groom (Prof. T. T.) on the igneous
rocks of the Malvern hills, 151.
Guggenheimer (Dr. S.) on the spark-
discharge, 311.

Gunn (W.) on the geology of the
Isle of Arran, 158.

Harmer (F. W.) on the influence of

winds upon climate during the
Pleistocene epoch, 577.

Heat, on the dynamical theory of, 1.
Hill (B. V.) on accidental double-
refraction in liquids, 524.

Hill (J. B.) on the crush-conglome-
rates of Argyllshire, 579.
Hilton (H.) on van der Waals'
equation, 108.

Hind (Dr. W.) on the beds below
the millstone git at Pendle Hill,

Howe (J. A.) on the beds below the
millstone grit at Pendle Hill, 154.
Hydrogen, on the spectra of, and

some of its compounds, 370; on
the isothermals of, 651.
Indiarubber, on the effect of an
alternating electromotive force on
the insulating properties of, 501.
Induction, on magnetic, in iron and
other metals, 456.

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