JuNE 26, 19c2] 
NAIURE 
213 
by D. P. Tudd.—On the occurrence of uranophane in Georgia, 
by T. L. Watson.—The internal structure of cliftonite, bys 
J. M. Davison. The view of Fletcher that this form of crystal- 
lised carbon is a psexdomorph after pyrite is not confirmed by 
these experiments. 
Journal of Botany.—The June number opens with notes on 
Mycetozoa by Mr. Arthur Lister, F.R.S., and Miss G. Lister. 
Two species are figured and described; of these Physarum 
gyrosum is allied to Fuligo septica, while the other, Chondrio- 
derma asteroides, is a new species which was found on pine 
needles and acacia leaves at La Mortola. In addition, the 
nomenclature of certain Mycetozoa collected by Dr. Celakovsky 
in Bohemia is discussed and revised. To the lists of Sussex 
plants already published by Mr. E. S. Salmon and Mr. Whit- 
well during the past half year is added another referring mainly 
to the west Arun district of west Sussex, contributed by Rev. 
E. S. Marshall. The catalogue of British marine algz com- 
piled by Mr. Batters which began in the March number has 
now reached the genus Ectocarpus. 
SOCIETIES AND ACADEMIES. 
LoNnpDON. 
Royal Society, May 15.—‘*On Microscopic Effects of 
Stress «n Platinum.’’ By Thomas Andrews, F.R.S., F.C.S., 
and Charles Reginald Andrews. 
The microscopic effects of stress on platinum do not appear 
Fic. 2.—Magnification 250 diameters. 
Microscopic effects of compressive stress on platinum showing 
crystalline slip as seen in section. 
Arrow indicates direction of compressive force. 
to have been studied. An ingot of pure platinum was therefore 
prepared, and from this a portion was accurately machined in 
the form of a cube, 0°30 inch square, which was afterwards 
NO. 1704, VOU. 66] 
carefully microscopically polished and then subjected to com- 
pressive stress in the testing machine. 
Prior to the application of stress, and for comparative pur- 
poses, a polished face of the platinum cube was microscopically 
examined, but an even polished surface only was observed. A 
force producing a compression of 10 per cent. on the total 
height of the cube was then applied, and microscopic observa- 
tions were taken at high magnifications of the effects of the stress 
on the microcrystalline structure of the platinum cube. 
The polished side of the cube upon which the high-power 
microscopic examination was made was the one in line, or in 
parallel, with the direction of the compressive force. 
Owing to the varied orientation of the different crystals in the 
mass of the platinum, the lines of cleavage as indicated by the 
minute ‘slip bands,” were often seen at varied angles to the 
line of the straining force. 
The general appearance of the disintegration of the large or 
primary crystal grains, produced by the pressure, on the pure 
platinum cube, was the apparent breaking up of the crystalline 
structure of the metallic mass, as seen in section, roughly 
diagonally to the line of the compressive force. The area 
enclosed by the main lines of disruption roughly approximating 
to the size of the large primary crystal grains. 
The distances between the extremely fine lines, or ‘slip 
bands,” appeared roughly to coincide proportionately with the 
size of the secondary or most minute crystals forming the mass, 
the finer ‘‘slip bands” appearing to indicate the crystalline 
slip which had taken place along the facets of the smaller or 
secondary crystals. The direction, however, of the main lines 
of the crystalline disruption did not appear always to coincide 
with the intercrystalline facet junctions of the large or primary 
crystal grains. The lines of least’ resistance, or greatest 
crystalline slip, seemed chiefly to develop at an approximate 
angle of about 45 degrees to the pressure line, as previously 
mentioned ; but the line of greatest weakness in the mass 
structure of the metal was not always at that angle with the 
line of the disruptive force. 
The authors hope that these experiments may prove of use in 
affording an indication of the comparative behaviour of the 
noblest metal platinum, with the behaviour of the constructive 
metals, copper, nickel, iron and steel, when under the influence 
of stress; and the experiments have also shown that the 
microscopic influences of stress in the heavy metal platinum are 
analogous to those which have been observed in metals of lower 
specific gravity. 
June 5.—‘‘ Contributions to the Study of Flicker.” 
By T. C. Porter, M.A., Eton. 
Rayleigh, F.R.S. 
This paper is the sequel to that already published in the 
Proceedings, vol. \xiii. It first details various precautions 
which experiments, carried out since that paper, have shown 
to be necessary in estimating the rate at which a black disc with 
a white sector must be rotated in order that the sensation of 
flicker may just vanish. Results are given which prove that 
the central portion of the retina is less sensitive to flicker than 
its outer region. The effect on the flicker of the measured 
want of blackness in the black sector is also discussed. The 
most important results of a long series of experiments, in which 
many observers took part (in order to eliminate as far as pos- 
sible the personal equation), is to prove that, if 7 be the number 
of rotations per second of the disc when flicker just vanishes, 
the angular magnitude of the white sector being kept constant, 
but the illumination of the disc being varied, by altering its 
distance from a measured and constant illuminant, then 
n= a+ 6 log I, where ais aconstant, and 4 is also a constant 
for all illuminations between a very feeble one and one under 
which the disc becomes almost unbearably bright. A full 
description of the illuminants used and of the measurement of 
the illuminations caused by them on the disc is given in the 
paper. At very low illuminations it is proved that the value of 
6 changes with unexpected rapidity, apparently becoming again 
constant. The bearing of the above equation on the practical 
value of the flicker photometer, and also the number of kine- 
matograph photographs which must be projected on a screen 
per second in order to get rid of flicker, is stated. 
The second important result is the experimental determination 
of 2, when the illumination of the disc is kept constant, but its 
apparent brightness is altered by altering the angular magnitude 
of the white sector. If this last, measured in degrees, is called 
w, the magnitude of the black sector will be 360 —w, and if 
Paper ii. 
Communicated by Lord 
