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FEBRUARY 19, 1914| 
NATURE 
793 
vard (5,627), Cornell (5,612), New York University 
(5,508), and Illinois (5,259). The largest number of 
officers is found at Columbia, where the staff of 
_ teaching and administrative officers consists of 907 
members, as against 737 at Illinois, 731 at Harvard, 
725 at Cornell, and 633 at Wisconsin. 
SOCIETIES AND ACADEMIES. 
Lonpon. 
Royal Society, February 12,—Sir William Crookes, 
O.M., president, in the chair.—S. G. Brown ; Chemical 
action that is stimulated by alternating currents. This 
paper describes experiments on the effects produced 
by passing a rapid alternating current through simple 
voltaic cells, the general effect being to stimulate 
chemical action and to cause the cells to give a greater 
supply of continuous current which otherwise would 
not be produced.—R. D. Oldham: The effect of the 
Gangetic alluvium on the plumb-line in northern India. 
The depression occupied by the Gangetic alluvium 
along the southern face of the Himalayas, as deter- 
mined by geological observation, has a nearly vertical 
face on the north, and a floor sloping upwards in a 
southerly direction to the surface. The effect of the 
defect of mass in the Gangetic depression is calculated 
and shown to be capable of producing about 30” of 
northerly deflection of the plumb-line at the margin of 
the range, a deflection which drops rapidly on either 
side of the margin, but more rapidly to the south 
than the north. At twenty to thirty miles south, the 
distance depending on the width of the trough, it 
becomes zero, and at greater distances is replaced by 
a southerly deflection.—G. W. Walker: Note on the 
origin of black-body radiation.—Prof. H.~M. Mac- 
donald: The transmission of electric waves along the 
earth’s surface. A series is obtained which represents 
the magnetic force at any point on the surface when 
the oscillator is also on the surface; the series con- 
verges rapidly for large values of 6, and for not very 
large values the first term is a sufficient approxima- 
tion. For small values of @ the series converges very 
slowly.—Dr. G. T. Beilby : Transparence or translucence 
of the surface film produced in polishing metals (see 
page 691).—Dr. S. W. J. Smith and J. Guild: A 
thermomagnetic study of the eutectoid transition point 
of carbon steels. The magnetic properties of steel at 
temperatures near the eutectoid transition point (Ar) 
seemed to deserve further examination. Simultaneous 
observations of intensity of magnetisation and of tem- 
perature were made over various ranges of heating 
and of cooling in different magnetic fields. Nine 
steels containing percentages of carbon ranging be- 
tween o-1 and 1-5 were used. Each steel contained 
about 0-2 per cent., or less, of silicon and manganese. 
It was found that the temperature corresponding with 
the beginning of the transformation of the eutectoid 
during heating (Ac1) could be fixed within +1° C. 
under suitable conditions. This temperature was 
735° C., and was the same for all the steels.—W. R. 
Bousfield : Note on osmotic pressure. It is shown that 
the assumption that the molecular interspaces of a 
solution are filled with vapour, which there behaves 
as a perfect gas, leads to the same general relation 
between vapour pressure and osmotic pressure as is 
given by thermodynamical considerations. The 
anomalous fact that the osmotic pressure of a deci- 
normal sucrose solution is found to be greater at 
o° C. than at 5° C. is explained by reference to the 
constitution of water and the effect of compression 
upon the ice molecules. 
Physical Society, January 23.—Prof. C. H. Lees, vice- 
president, in the chair.—P. R. Coursey: Some char- 
acteristic curves and sensitiveness tests of crystal and 
NO. 2312, VOL. 92] 
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other detectors. Experiments were described recently 
conducted on types of wireless detectors, and under- 
taken with a view of finding out whether any relation 
could be traced between the, sensitiveness and char- 
acteristic curves of a detector. Sample curves for 
some common detectors are included, and show that 
in some cases a fairly good agreement exists between 
the sensitiveness curve of a detector and the second 
differential of its characteristic, this being most notable 
in stable crystal detectors, but it is evident that the 
flexure of the characteristic curve cannot be the only 
cause of the response of a detector to wireless signals, 
but that at least a second action must also be present, 
as it was observed, notably in the electrolytic detector, 
that the maximum ordinates on the second differential 
were at places where the measured sensitiveness was 
either zero or extremely small, showing that there are 
probably two actions opposing one another at this 
point. This action when present in other detectors 
is perhaps electrolytic in nature, or the received oscilla- 
tions when superimposed on the direct-current boost- 
ing voltage partake of the properties of some 
“trigger ’’ action. This view is supported by experi- 
ments with detectors of the tellurium-aluminium type. 
—W. Duddell: A water model of the musical electric 
arc.—C. R. Darling: Further experiments with liquid 
drops and globules.—James Walker: A note on aberra- 
tion in a dispersive medium, and Airy’s experiment. 
Lord Rayleigh’s view that in the case of aberration we 
are concerned with the group-velocity instead of with 
the wave-velocity, makes it necessary to consider the 
experiment of Airy, in which he measured the angle 
of aberration with a telescope filled with water. A 
modification of Lord Rayleigh’s explanation leads to 
the result that the angle of aberration thus determined 
corresponds to an angle p—'v/U measured in air. 
The same result is obtained from an analytical inves- 
tigation, and a numerical calculation shows that the 
increase in the angle is about 1 per cent.—an amount 
that is probably too small to be detected. 
Mineralogical Society, January 27.—Dr. A. E. H. 
Tutton, president, in the chair.—T. Crook: 
The genetic classification of rocks and ore deposits. 
The general principles of the classification of rocks 
were considered, the term rock including all mineral 
deposits. The exact nature of genetic grouping was 
defined. Both rocks and ore deposits fall into broad 
natural divisions in accordance with a _ geological 
grouping of formative agents and processes, the type 
being determined by the last operative agent or pro- 
cess that gave the rock its individuality. The two 
main groups are (1) endogenetic deposits, arising from 
internal causes, and (2) exogenetic deposits, of super- 
ficial origin, and these are subdivided in a consistent 
genetic manner. ‘‘ Sedimentary ’’ and ‘‘ metamorphic ”’ 
products cannot be regarded as constituting two in- 
dependent subdivisions. A historical review of the 
application of genetic-geological principles to the 
classification of rocks and ore deposits was included. 
—Prof. A. F. Rogers: Lawsonite from the central 
coast ranges of California, Crystals from new 
localities were described; prismatic and tabular in 
habit and usually small, they displayed the forms oro, 
oor, o11, 110.—A, F. Hallimond; Uniaxial augite 
from Mull. The small, lath-shaped crystals, which 
seldom exceed 4 mm. in diameter, have refractive 
indices 0 1-714, e 1-744, specific gravity, 3-44, pro- 
nounced dichroism (o smoky-brown, e pale yellow), 
two cleavage directions nearly at right angles, and 
an extinction angle of 303° on the cleavage. A chem- 
ical analysis revealed distinct differences from ordinary 
diopside, and the composition approximates to that 
of hypersthene—H. H. Thomas and W. Campbell 
Smith: Apparatus for grinding crystal plates and 
