286 
NATURE 
[May 106, 1912 
primary beam. (2) The absorption coefficient of the 
more penetrating part of the reflected beam decreases 
with increasing thickness of the reflector. (3) The 
final absorption coefficient of the rays reflected from 
thick sheets of aluminium, copper, and lead are 33-7, 
26-6, and 20:2 cm.~1 respectively. (4) The coefficient 
of absorption of the easily absorbed part of the radia- 
tion reflected by aluminium is about 235 cm.—'. The 
absorption coefficients of the corresponding rays re- 
flected from copper, lead, and air have not been deter- 
mined with any degree of accuracy, but are of the 
same order of magnitude as that of the rays reflected 
by aluminium. (5) An expression has been obtained 
for the variation of the amount of reflected radiation 
with the thickness of the reflector, and has been 
shown to be in good agreement with the results 
obtained experimentally by Schmidt. 
Geological Society, May 1.—Dr. Aubrey Strahan, 
F.R.S., president, in the chair.—P. Lake and Prof. 
S. H. Reynolds: The geology of Mynydd Gader, Dol- 
gelly; with an account of the petrology of the area 
between Dolgelly and Cader Idris. Mynydd Gader 
lies immediately south of the area described by the 
authors in a previous paper (Q.J.G.S., vol. lii., 1896, 
pp. 511-21). The Tremadoc beds are here succeeded 
by a group of rocks which are, for the most part, 
of volcanic origin. These may be divided into a 
rhyolitic series below and an ashy series above. The 
rhyolitic series is formed chiefly of lava-flows; the 
ashy series consists mainly of volcanic ashes and 
slates, the ashes predominating below and the slates 
above. Didymograptus bifidus occurs near the base 
of the ashy series, D. murchisoni in the upper part. 
The rhyolitic series appears to be older than the main 
mass of volcanic rocks in the Arenig area, but it may 
be contemporaneous with the Calymene ashes of that 
district. It is probably of approximately the same age 
as the volcanic series of Skomer Island, and the fact 
that in both places the rhyolitic rocks are soda-rhyo- 
lites is of considerable interest. HH. Bolton: Insect- 
remains from the midland and south-eastern coalfields. 
The writer describes a series of three insect-wings 
obtained by Dr. L. Moysey from the Shipley clay-pit 
near Ilkeston (Derbyshire), and a blattoid wing, and 
three fragments from the borings of the Kent Coal 
Concessions Company, Ltd., in East Kent. The first 
series of insect-wings occur in greyish-brown iron- 
stone nodules, which lie in bands in a yellow clay 
about 30 or 4o ft. below the top hard coal. The East 
Kent insect-remains occur in core shales, the horizon 
of which is not yet determined. The East Kent 
insect-remains contain one wing, referable to the 
genus Soomylacris (Ettoblattina), a species of which 
is already known from the Forest of Dean coalfield. 
The finding of two species of the same genus in coal- 
fields so widely separated as those of the Forest of 
Dean and East Kent is not without interest, in view 
of the generally-accepted belief in the former con- 
tinuity of the Coal Measures across the south of 
England. 
Linnean Society, May 2.—Dr. D. H. Scott, F.R.S., 
president, in the chair.—Miss T. L. Prankerd: The 
structure of the Palzozoic seed Lagenostoma ovoides, 
Will.—Dr. Karel Domin: Additions to the flora of 
western and north-western Australia. The account 
was drawn up from undescribed material in the her- 
barium of the Royal Botanic Gardens, Kew, consist- 
ing chiefly of collections by Dr. E. Clement and 
Captain A. A. Dorrien-Smith. Beside many new 
varieties, the author characterises fourteen new plants, 
one being Casuarina dorrieni, eight grasses, three 
being species of Panicum, and five other Monocotyle- 
dons.—G, H. Wailes : Fresh-water Rhizopoda from the 
NO. 2220, VOL. 89] 
1 C., and 01385 x 10-° for 
| States of New York, New Jersey, and Georgia, with 
a supplementary account of some species from the 
Seychelles. The gatherings forming the basis of the 
present paper were collected in the autumn of 1o1r; 
the Rhizopod fauna is summed up as being rich in 
species and individuals, about 80 per cent. being 
similar to those found in Europe. The remainder of 
the paper was devoted to a systematic account of the 
species found, including three new species of Nebela, 
one of Euglypha, and many varieties. 
Physical Society, April 26.—Mr. A. Campbell, vice- 
president, in the chair.—The adjourned discussion on 
Mr. H. Donaldson’s paper on the coefficients of 
expansion of fused silica and mercury was re- 
sumed. Prof. H. L. Callendar opened the discussion 
by communicating a paper on the expansion of 
vitreous silica. The expansion of vitreous silica at 
ordinary temperatures had acquired special interest 
recently in connection with mercurial thermometry 
and standards of length and expansion. The majority 
of observers had used the Fizeau method with 
specimens 10 mm. to 15 mm. long. Somewhat 
different values had been found for different specimens 
with different standards of comparison. For a cylin- 
drical specimen on a platinum-iridium tripod Chappuis 
found 50x10-® for the expansion from 0° C. to 100° 
the coefficient at 0° C. 
Scheel, for a similar specimen, tested against a quartz- 
crystal ring, found 455 x 10-® from o° C. to 100° C., 
and 0°217x 10~-° at o° C. For a ring specimen tested 
in a vacuum by the absolute method he found values 
almost identical with Chappuis; but Randall, employ- 
ing a similar ring specimen, also made by Zeiss, found 
the mean coefficient from 16° C. to 80° C. (which is 
nearly the same as that from o° C. to 100° C.) to be 
only 0424 10-°. Such differences might be due to 
accidental errors, or to differences in form and treat- 
ment of the specimens employed, or to differences in 
the standards of comparison. But since the whole 
expansion of 1 cm. of fused silica between 0° C. and 
100° C. was only of the order of one wave-length of 
light, it was also possible that small constant errors 
might arise in so delicate an experiment from gas- 
films or other surface effects variable with tempera- 
ture. It seemed, therefore, desirable to measure the 
expansion of the long silica rods at low temperatures 
by a direct interference method in which such sources 
of error were excluded. The method used gave a 
smaller and more rapidly diminishing value for the 
expansion of the silica rods than that obtained by 
other observers employing the orthodox Fizeau method 
with short specimens. With the assistance of Mr. A. 
Eagle, the author had made some observations on the 
difference between the radial and axial expansion of a 
silica tube similar to that from which the bulbs of the 
mercury weight thermometers employed by Harlow 
and Eumorfopoulos had been constructed. Three sets 
of determinations had been made by Mr. Eagle on 
three different days with closely concordant results. 
The mean of these showed that the axial coefficient of 
expansion of the specimen tested exceeded the radial 
coefficient by 0'20 x 10-® over the range 18° C. to go® 
C. This result agreed as closely as could be expected 
with the values of the cubical coefficient deduced from 
the weight thermometer observations of Harlow and 
Eumorfopoulos when the values of Callendar and 
Moss for the absolute expansion of mercury were 
assumed.—R. Appleyard: The solution of network 
problems by determinants. The paper is a practical 
application of the method described before the Physical 
Society in 1885 bv Dr. J. A. Fleming. Let it be 
supposed that cyclic currents have been assigned to 
all the meshes of a given network, and that all 
capacities (K, in farads), inductances (L, in henries), 
