222 
primary oral tentacles arise directly from it, alternating 
with one another. The internal madreporite arises as 
a secondary differentiation of the walls of the stone- 
canal.—R. E. Turner: Wasps of the genus Pison. One 
hundred: and nine species are dealt with, of which 
fifteen are described as new. Reasons, drawn from 
the numerical distribulion of the species in different 
areas, are given for supposing the genus to be in a 
declining state—fifty of the total number of species 
being from the continent of Australia. In addition to 
Pison, the small allied genera, Aulacophilus and Pison- 
opsis, are dealt with, one new species of the former 
being described. 
Physical Society, October 27.—Mr. F. E. Smith, vice- 
president, in the chair.—Dr. S. G. Barker : The applica- 
tion of the Kerr effect to the determination of the 
saturation values for magnetism of ferro-magnetic 
metals, compounds, and alloys. The paper describes 
work carried out in the laboratory of Prof. Du Bois 
on the relation between the intensity of magnetisation 
of various ferro-magnetic materials and the rotation 
of the plane of polarisation of plane polarised light 
reflected from a polished surface of the material. 
The specimens, in the form of circular discs 5 mm. 
in diameter and o-5 mm. thick, were soldered to one of 
the pole pieces of a large electromagnet. Through an 
aperture in the other pole monochromatic light, 
polarised in two nearly coincident planes by means of 
a Lippich polariser, was incident almost normally on 
the polished surface of the specimen. The reflected 
beam passed through an analyser, the rotation of 
which could be measured, by means of an auxiliary 
optical system, to a high degree of aécuracy. In the 
first part of the paper results are given for a number 
of materials of known magnetic properties in order to 
establish the validity of the method, due to Du Bois, 
of obtaining the value of the saturation intensity from 
the curve connecting field strength with rotation. The 
method is then applied to materials of unknown pro- 
perties. The variation of the Kerr constant with the 
wave-length of the light was also determined for a 
number of substances.—D. Owen: The influence of the 
time element on the resistance of a solid rectifying 
contact. The resistance at a solid rectifying contact, 
and consequently the exact shape of the resistance 
characteristic, depend upon the time for which the 
testing current is allowed to flow. A series of char- 
acteristics is given corresponding to durations of con- 
tact extending over the range one forty-thousandth of 
a second to thirty seconds. The following conclusions 
are drawn :—(1) That the variation of resistance with 
voltage may be attributed entirely to thermal effects. 
(2) That the characteristic obtained by applying the 
testing voltage for one hundredth of a second is, at 
moderate voltages, materially the same as that which 
would be found at the expiry of a period of the order 
of a millionth of a second. (3) That the sensibility of 
a wireless receiving circuit (in which the rectifying 
contact is used) does not differ very appreciably from 
that deduced from a slow period characteristic. (4) 
That an important fraction of the contact-resistance 
resides in a stratum of molecular thickness at the 
interface of the two elements of the contact; and that 
it is in this region alone that rectifying action at very 
high frequencies is effected. 
Linnean Society, November 2.—Sir David Prain, presi- 
dent, in the chair.—Prof. G. S. Boulger : Early chapters 
in plant distribution. The author sketched the first 
glimpses in the works of Cardinal Bembo, M,. de 
VObel, Sir Hans Sloane, Dr. Christian Mentzel, and 
J. Pitton de Tournefort. The second chapter was 
devoted to Carl von Linné, whose ‘‘ Flora lapponica”’ 
and several theses in the ‘‘Amoenitates academicz ” 
were brought forward in support. Next followed 
NO. 2455, VOL. 98] 
NATURE 
| individual in the racial experience. 
| meeting.—Mr. W. Barlow,. president, in the chair.— 
- . «ee 
fe 
[NovEMBER 16, 1916 
Haller, J. G. Gmelin, Buffon and Forskl , C. L. 
Wildenow, with a brief allusion to P. A. Broussonet.— 
L. A. Borradaile: The Pontonjine and Carides from 
the western Indian Ocean. 
Aristotelian Society, November 6.—Dr. H. Wildon 
Carr, president, in the chair—Dr. H. Wildon Carr: 
Presidential address: The problem of recognition. In 
the experience of recognition there is an element which 
may be named “‘againness.”” The problem of recog- 
nition is the nature and genesis of this element. There 
are two forms of recognition, in each of which we 
meet with this element of ‘‘againness '’—an intelligent 
form and an instinctive form. These appear to be 
quite separate, but the cognitive fact is the same in 
each. In intelligent recognition we seem able to 
account for the ‘‘againness’’ by repetition, memory, 
and the judgment or perception of identity or simi- 
larity—the mental process being an external act of 
comparison between a present sense-datum and a past. 
This, however, is an illusion, because in reality the 
essential factor, repetition, is absent. Recognition 
implies prior cognition, but does not depend on the 
presence of a memory-image of the prior cognition. 
Recognition is the conditionate, and not the condition, 
of learning by experience; learning by experience is a 
primary, not a dependent, fact. In instinctive recog- 
nition there can be no memory-image of the prior 
cognition, because this prior cognition lies beyond the 
Yet in instinctive 
recognition we have sentience, familiarity, and pre- 
awareness—all of which are mental characteristics. 
We have, therefore, to conceive the mental process, 
or the mind, as a continuous organisation of experi- 
ence. Past experience has not only contributed its 
quota to this organisation, but is incorporated within 
it, giving to it, and receiving from it, its character 
and individuality. New sentient experience in enter- 
ing this organisation receives the impression of its 
stamp or mould, and this is the mark of the past on 
the present cognition which constitutes it recognition. 
Mineralogical Society, November 7.—Anniversary 
Dr. J. W. Evans: The combination of twin operations. 
The question of complex twin-crystals in which two 
distinct laws of twinning are represented was dealt 
with. A distinction was made between cases in which 
the twin-axes are parallel or at right angles, and those 
in which they are inclined to one another obliquely. 
In the former the result of the combination is itself 
a twin operation, while in the latter it is a rotation, 
the direction of which depends on the order in which 
the operations are applied; it is in some cases combined 
with an inversion.—Dr. J. W. Evans: A modification 
of the Kohlrausch method of determining refractive 
indices. The observing instrument is a micros 
placed vertically and fitted with a Bertrand lens. An 
immersion theodolite stage of the Klein type is used 
so that the substance under investigation may be 
rotated beneath a liquid of higher refractive index 
about two axes, the first at right angles to the optical 
axis of the instrument, and the second at right angles 
to the first and to the plane surface of the object. 
This is observed through the natural surface of the 
liquid, and rotated in either direction until the position . 
of total reflection is reached. By rotation of the object 
about the second axis the refractive indices in all direc- 
tions parallel to its plane surface may be determined, 
and the values of the principal refractive indices thus 
obtained.—A. Holmes and Dr. H. F. Harwood; The 
basalts of the Brito-Arctic Province. The basalts from 
Hare Island, which were collected by Thomas Reid in 
1855, include six varieties, of which four are free from 
olivine and carry silica among the amygdale minerals, 
and the remaining two contain olivine and are with- 
