346 

Societies and Academies. 
Lonpon. 
Royal Society, March 1.—A. Mallock: The effect 
of temperature on some of the properties of steel. 
The period of torsional vibration and the length of 
a steel wire were automatically and continuously 
recorded in terms of time, while the temperature 
was varied between 15° and 1000° C. The results 
show (1) that the variation of the rigidity of steel 
between ordinary temperature and a dull red heat 
is small (less than 1 per cent.) ; (2) that above the 
critical temperature (about 800° C.) the rigidity 
decreases rapidly; (3) that the temperature co- 
efficient of expansion does not show any marked 
change as the metal passes through the critical 
temperature ; but (4) that a comparison with the 
cooling curves of iron and steel proves that the 
specific heat of the high temperature form of the 
metal is much less than it is at temperatures below 
the critical point.—C. H. Lees: Inductively coupled 
low-resistance circuits. The oscillations in each of 
two circuits of low resistance coupled by their mutual 
inductance can be simply expressed in terms of a 
certain product of capacitance and inductance, 
The expressions for the currents lead to a simple 
graphical solution of the problem.—Lord Rayleigh : 
Studies of iridescent colour, and the structure pro- 
ducing it——(1) The colours of potassium chlorate 
crystals. The structure of the iridescent potassium 
chlorate crystals investigated by Stokes and the 
late Lord Rayleigh is examined microscopically. 
The periodic twinned structure inferred by the latter 
is clearly shown in the photographs taken under 
the microscope with polarised light. Some crystals 
have exceedingly complex structure, showing many 
groups of evenly spaced twin planes and a very 
complex reflection spectrum. This results from high 
interference from twinned layers situated a consider- 
able distance apart. Chlorate crystals, giving a 
silvery reflection, were obtained by Madan, who 
heated the ordinary colourless crystals to about 
250° C. A complex twinned structure is induced, 
and photographs of the structure of the crystal and 
of the reflection spectrum show corresponding 
irregularities in each, resulting from want of flatness 
in the twin planes. (2) Mother-of-pearl. The results 
generally confirm those of Brewster and A. H. Pfund. 
Micro-photographs show the grating structure of a 
pearl oyster shell and the structure of parallel layers 
of an “ear ”’ shell. The absorption spectrum of the 
latter shows that in agreement with the spacing of 
the layers the reflection is of the second order. 
(3) The colours of Labrador felspar. The colours 
seen by reflection arise from two distinct origins :— 
(2) Specular reflection from tabular inclusions, which 
show the colours of thin plates and are often 0-2 mm. 
in dimensions ; they are distributed parallel to one 
of the cleavages. (4) Diffuse reflection from a plane 
about 15° away from the cleavage mentioned ; this 
is the source of the striking colours observed. When 
the diffuse reflecting plane is examined microscopically 
under conditions which ensure that the light only 
comes from a very thin stratum, it is found that the 
plane of reflection is patchy. The patches are of 
irregular outline. The diffuse character of the 
reflection is accounted for by the small diameter 
of these reflecting surfaces, regarded as independent 
optical apertures. Their size (0-005 mm.) accounts 
approximately for the angular diameter of the diffuse 
image of a point source seen by reflection. The 
colour of the reflection is not sharply limited to special 
regions of the spectrum, and can be explained by 
the interference of streams of light from the two 
NO. 2784, VOL. 111] 
NATURE 

[Marcu 10, 1923, 

surfaces of each patch. The patches may be fissures 
in the material, and there is evidence that their 
thickness is not absolutely uniform, The brightness 
of the colour is explicable by the large number of 
reflecting patches adding their effects, without 
definite phase relation suchas would give rise to 
regular interference.—L. V. King: On the complex 
anisotropic molecule in relation to the dispersion and 
scattering of light. 
Society of Public Analysts, February 7.—Mr. P. A. 
Ellis Richards, president, in the chair.—E. Griffiths- 
Jones: Titanium in Nile silt. Titanium is determined — 
by a colorimetric method after freeing the sample 
from silica ; 1-3-2°55 per cent. of titanium oxide was 
found. Egyptian straw showed only 0-4 per cent. of 
titanium oxide on the ash.—Osman Jones: Notes on 
the examination of preserved meats, ete. The 
presence of a trace of zinc chloride in the tin container 
(which sometimes arises through the use of this salt 
as a soldering flux) causes a more rapid absorption 
of tin by the food contents ; the use of sealing fluid 
containing a high boiling-point solvent also causes 
a disagreeable flavour to be imparted to the food 
material. The absorption of tin by the meat contents 
of a can is greatest at the time of processing and 
almost ceases after about 4 months. A dilute 
solution of iodine in potassium iodide gives a crimson 
colour with agar, while with gelatin an orange- 
coloured precipitate is produced. 
Optical Society, February 8.—F. W. Preston: 
On the properties of pitch used in working optical 
glass. Pitch as a material for mounting lenses for 
polishing possesses many remarkable advantages. 
Its colour is valuable; the dull black surface in 
contact with the lens prevents reflection of light at 
the second face of the glass. Its coefficient of 
expansion approximates to that of glass, it melts 
at a relatively low temperature, and remains plastic 
through a considerable range. Pitch, being an 
undercooled liquid, may be made sufficiently solid 
to resist deformation by external pressures during 
the polishing operation, and yet left oe 
plastic to yield to internal stresses, so as to be self- 
annealing at ordinary temperatures. The alteration 
of properties on prolonged heating is its most serious 
disadvantage—T. Y. Baker: Prismatic astrolabe 
designed and made at the Admiralty Research 
Laboratory, Teddington. This instrument, used for 
accurate geodetic survey work, is a modification of 
that designed by MM. Claude and Driencourt, which 
has been extensively used in Egypt. The modifica- 
tions are: (i.) The prism can be rotated about an 
axis parallel to its edges, and the angles of the prism 
are allowed to depart slightly from 60°; by using 
each edge of the prism in turn as the front edge, 
three observations of the star can be made instead 
of only one, the mean of the measured altitudes 
being exactly 60°. (ii.) A refracting prism of small 
angle is mounted to cover one quadrant of the object 
glass and a duplicate image of one star is thus 
produced in the field of view. The duplicated images 
are on the same horizontal level. Observation for 
contact is made by noting the instant when the 
descending image is on a level with and between the 
duplicated images. Laboratory trials show that 
whereas the mean error of observation with the old 
scheme was 0-2”, with the new arrangement it is 
o:12”. : 
Aristotelian Society, February 19.—Prof. Wildon 
Carr in the chair.—C. E. M. Joad: The problem of 
free will in the light of recent developments in 
philosophy. It is generally admitted that on the 
basis of the Materialist and Mechanist theories, the 
