2 
DEcEMBER 28, 1916] 
large superficial root-system of adventitious origin 
derived from the lower half of the hypocotyl. In 
plants in which the first and subsequent nodes trail 
along the ground, additional roots are produced from 
these. Abortive roots commonly arise at the bases of 
lateral branches, and further development can be in- 
duced also in these by suitable manipulation. Various 
other factors, such as wounding, increasing the height 
of the soil, etc., also induce accessory root-formation. 
—Miss A. J. Davey and Miss M. Gibson: The distribu- 
tion of moneecious plants, and the occurrence of herm- 
aphrodite flowers in Myrica Gale, with observations 
on variations of sex. M. Gale, the common bog 
myrtle, is described as being typically dioecious, but 
mention has been made by several authors of the occa- 
sional occurrence of the moncecious condition. Obser- 
vations during several successive years on a large area 
of Myrica in the peat moors of Somerset show that 
there isalways asmall proportion of moneecious plants, 
which present all gradations between the normal pistil- 
late and staminate types. Further, it has been found 
that the sex of a plant may vary from year to year. 
Optical Society, December 14.—Mr. F. J. Cheshire, 
president, in the chair——L. C. Martin: The refracto- 
metry and identification of glass specimens, especially 
lenses. The determination of the refractive index 
generally requires at least one plane-polished surface 
in the specimen, but the method described could be 
used for lenticular, irregular, or unpolished pieces of 
glass. By immersing the specimen in a liquid of equal 
refractive index the system became optically homo- 
geneous for light of a particular wave-length. |The 
liquid, which may be a mixture of carbon disulphide 
and alcohol or a solution of mercuric potassium iodide, 
is contained in a prism cell on the table of a spectro- 
meter, and is kept mechanically stirred. Spectra from 
the usual sources are observed by refraction through 
the prism, of which the sides are plane parallel glass. 
The introduction of the specimen diffuses the light, 
but any particular spectrum line may be focussed by 
adjustment of the strength of the liquid. The refrac- 
tive index of the liquid and specimen is then found 
in the usual manner.—Dr. R. S. Clay: A workshop 
method of determining the refractive index of a block 
of glass of which only one face is polished. The 
method was shown to be based, as are the Abbe and 
Pulfrich refractometers, upon the determination of the 
critical angle when light passes from the medium of 
which the refractive index is to be found into one of 
which the index is known. The hemispherical ball of 
Abbe or the cube of the Pulfrich refractometer is 
replaced by an isosceles right-angle prism. This must, 
of course, have a higher refractive index than that of 
the substance it is required to measure. A simple 
telescope, composed of two spectacle lenses with a cross- 
wire at their common focal plane, is used to take the 
readings. A drop of liquid of high refractive index 
(e.g. quinoline or oil of cassia) is placed on the hypo- 
tenuse face of the prism, and this is placed upon the 
polished face of the glass of which the refractive index 
is required. Sodium light is caused to fall on one side 
of the block of glass, and the light emerging from one 
face of the prism is received by the telescope. The 
latter is turned until the critical angle is obtained, 
shown by one-half of the field of the telescope becom- 
ing black, and the dividing line of the field being on 
the cross-wire of the telescope. The observation is 
repeated for light falling on the opposite side of the 
glass block, and emerging from the other face of the 
prism. The angular distance between the two posi- 
tions of the telescope determines the refractive index 
of the glass by a simple calculation, or the scale can 
be divided to give the refractive index directly. 
NO. 2461, VOL. 98] 
NATURE 
543 
Royal Meteorological Society, December 20.—Major 
H. G. Lyons, president, in the chair.—C, Salter: The 
measurement of rainfall duration. Save for an article 
by Mr. Baldwin Latham in 1880, practically no atten- 
tion appeared to have been paid to this subject until 
1903, when Dr. H. R. Mill commenced collecting re- 
cords for the British Isles, the number of which has 
grown until, in ‘‘ British Rainfall, 1915," as many as 
forty-eight records were published. An examination of 
these records revealed certain inconsistencies which 
were probably due to personal and instrumental causes. 
The differences appeared to be due principally to the 
varying degrees of sensitiveness of the recording instru- 
ments to very light rain, and the suggestion had been 
made that if rain of very low intensity were omitted 
from the records a closer approximation to homo- 
geneity would be attained.—Prof. H. H. Turner: Dis- 
continuities in meteorological phenomena: third note. 
In two previous papers it has been suggested that 
meteorological history is divided into definite chapters 
of average length 6} years, the separating dates being 
assigned according to a regular law. Further, that if 
these chapters are numbered consecutively those with 
even numbers differ in certain essential respects from 
those with odd numbers. The present paper gives the 
systematic analysis of fifty-five years’ monthly rainfalls 
at twenty-eight European stations. The division into 
alternating chapters is clearly brought out, and it is 
apparently possible to assign the separating dates from 
this material within a month. This precision is made 
possible by the existence of a five-monthly periodicity, 
for which some evidence was given in a former com- 
munication, but which is clearly established by the 
mass of evidence here submitted. The division into 
chapters has been connected in a former paper with 
the movements of the earth’s axis. In the present 
paper some earthquake statistics are put forward which 
appear to be favourable to this view. 
MANCHESTER. 
Literary and Philosophical Society, November 
Mr. T. A. Coward, vice-president, in the chair.—H. 
Bolton: The Mark Stirrup collection of fossil insects 
from Commentry, Central France. This collection of 
insects is now in the Manchester Museum, and was 
obtained by the late Mr. Mark Stirrup from his 
friend, Charles Brongniart, author of the classical 
memoir, ‘Recherches pour servir A histoire des In- 
sectes Fossiles des Temps Primaires.’”’ It consists of 
nine specimens, of which five are blattoids, one is a 
fragmentary wing of Goldenbergia (Microdictya) 
hamyi, two belong to new genera and species, and 
one is indeterminable. All the insect remains occur 
in a compact and thin flaggy mudstone. The blattoid 
wings belong to five species, of which two are refer- 
able to the genus Necymylacris, and three to the genus 
Phvlloblatta. Four of the species are new; the fifth 
is an example of Phylloblatta brongniarti of Hand- 
lirsch. Of the two new genera, one is considered to 
have close relationships with the family Perlida, 
whilst the second is regarded as an archaic type of the 
family Panorpide.—J. W. Jackson: Faceted pebbles 
from Pendleton, Lancashire.—Dr. F. E. Bradley: 
Presence of arsenic in baking-powder.—W. H. Todd: 
Behaviour of a blackbird. 
Dvs in. 
Royal Dublin Society, November 28.—Prof. G. H. 
Carpenter in the chair.—Prof. W. Brown: The fatigue 
of nickel and iron wires when subjected to the influ- 
ence of transverse alternating magnetic fields. The 
fatigue under these conditions is less than that due 
to longitudinal alternating magnetic fields by 5-5 per 
cent. for nickel and 25 per cent. for iron, and in both 
28.— 
