

Ss) 
May 5, 1923] 
hot junctions may have small heat capacity, the 
_ bi-metallic strips composing the thermopile are made 
of plates of constantan and manganin silver-soldered 
along an edge, rolled in a direction parallel to the 
edge into thin foil, and then cut into strips per- 
pendicular to the edge—C. W. Hume: A note on 
aberration and the Déppler effect as treated in the 
theory of relativity. Aberration has been explained 
as due to tne compounding of the velocity of light 
_ with the velocity of the earth relative to the ether; 
hence it appears to conflict with the principle of 
telativity. Simple methods are given of treating 
this problem consistently with the restricted principle, 
and of finding the Déppler effect. The result differs 
from the non-relativity result by terms of the second 
and higher orders in v/c.—C. R. Darling and C. W. 
Stopford : Experiments on the production of electro- 
motive forces by heating junctions of single metals. 
When a circuit is closed through a junction of a cold 
metal with a hot piece of the same metal, large electro- 
motive forces are often noticed ; e.g. a bare copper 
wire connected to the terminals of a galvanometer was 
cut at the middle, one of the cut ends heated and 
brought into contact with the cold end, and a large 
deflexion was obtained. Electromotive forces up 
to 0-25 volt may thus be produced.—R. H. Humphry : 
The double refraction due to motion of a vanadium 
mtoxide sol, and some applications. In linear 
ow the liquid behaves ia the same way as a plate 
of uniaxial crystal cut parallel to the axis and placed 
with axis parallel to the direction of flow. The 
field between crossed nicols lights up near an obstacle 
interposed in a stream of the liquid. Similar effects 
due to efflux of the sol from a jet, to the convective 
stream from an electrically-heated wire, etc., were 
also described. 
Optical Society, April 12.—Prof. A. Barr, president, 
in the chair—F. Twyman: The Hilger microscope 
interferometer. The instrument is used for measuring 
the aberrations of microscope objectives. A col- 
limated beam of monochromatic light is separated 
into two beams at the transmissively silvered surface 
of a plate of plane parallel glass. The transmitted 
beam’ passes through the lens under test, and is 
reflected back from the surface of a convex mirror, 
which coincides nearly with the approximately 
spherical wave front of the light as it converges 
er passage through the lens. The second beam 
is reflected back along its own path by a mirror so 
_that the two beams recombine at the silvered surface 
of the plane parallel plate. Portions of each beam 
then pass on together through a lens to the observer, 
who sees an interference pattern apparently located 
on the surface of the lens under test, which is a 
contour map, to a scale of half wave-lengths of the 
light used, of the aberrations of wave-surface caused 
in a plane wave.—A. Whitwell: On the form of 
the wave-surface of refraction. A series of wave- 
surfaces is drawn for each of a number of refracting 
surfaces or lenses. Each series consists of the 
following forms, which always follow each other in 
the same order. (1) Saucer type; convex to the 
incident light when the refracted pencil is converging, 
and concave when the pencil is diverging. (2) Saucer 
with inturned edges; like (1), but the edges of the 
wave-surface which have passed through the prim: 
focus are concave towards the incident light when 
the refracted pencil is converging. (3) Closed surface 
type; the wave-surface is completely closed like a 
cone with a dished bottom, the axis of the cone 
being coincident with the optic axis. (4) Goblet 
oad somewhat like a champagne glass set sideways, 
e bowl being towards the incident light and the 
base towards the secondary focus. (5) Basin type ; 
NO. 2792, VOL. 111] 
NATURE 
623 

the base of the goblet has disappeared and just 
beyond the focus the surface is like a basin concave 
towards the incident light. The diffraction spectra 
are found in the neighbourhood of the edges of the 
saucers, of the apex of the closed surface type, and 
of the rims of the goblet and basin type. Interference 
patterns occur in the region bounded by the caustic 
and by the extreme marginal rays. By drawing 
wave -surfaces half a wave-length apart lines of 
maximum and minimum intensity are found which 
are the sections of surfaces of revolution on which 
the intensity is a maximum or minimum. Sections 
of these surfaces by a plane at right angles to the 
axis show interference rings. The goblet type of 
wave-surface always occurs between the focus for 
marginal rays and that for paraxial rays, and may be 
called the characteristic of the focus. 
Linnean Society, April 19.—Dr. A. Smith Wood- 
ward, president, in the chair—aA. B. Rendle: The 
structure of the fruit of the mare’s-tail ( Hippuris 
vulgaris Linn.). The fruit is a drupe, the upper 
portion of which around the persistent base of the 
style, with the seedcoat, is developed in the form 
of a stopper which is easily withdrawn on soaking 
the ripe fruit. The embryo ultimately fills the seed, 
and has the large radicle and hypocotyl so often 
found in water plants. The radicle is placed directly 
beneath the stopper which provides a place of exit 
on germination.—B. Daydon Jackson: History of 
botanic illustration during four centuries (Colour). 
In the early years of printing, copper-plate’engraving 
was employed in providing outlines for hand-colouring 
and was in use until the last century, when it was 
ousted by lithography. In Redouté’s method of 
semi-stipple for coloured prints each colour was 
separately applied to the plate and cleaned off, 
before finally heating the plate and pulling the print. 
Chromo - lithography has greater permanence, if” 
lasting colours are employed, than hand-coloured 
plates. In the three-colour process three (or four) 
half-tone blocks are prepared, each to print its own 
colour, to give a complete colour scheme. The 
weakness of the process lay in this, that it almost 
demanded a paper coated with baryta or china-clay, 
which could not be guaranteed as permanent: in 
addition was the temptation to use inks, made from 
aniline dyes, which were fugitive. 
CapPpE Town. 
Royal Society of South Africa, March 21.—Dr. A. 
Ogg, president, in the chair—B. T. Schénland: On 
the passage of cathode rays through matter. The 
absorption, reflexion, and secondary emission involved 
in the passage of fast cathode rays through thin 
foils of various metals, and their variation with the 
velocity of the rays, were examined. Accurate 
measurements were possible up to 0-4 of the velocity 
of light. The results show that Lenard’s Law is 
only an approximation. The existence of a ‘‘ range ”’ 
for these particles appears to be established, two 
independent methods of measuring it agreeing very 
satisfactorily. The values obtained are in agreement 
with the theory of absorption due to Bohr.—T. 
Stewart: Holtzhuisbaaken Spring, Cradock. The 
spring is a typical Karroo spring. Measurements 
of the flow have been taken over a period of 38 years. 
The rainfall of a particular season is found to be 
reflected in the flow, but is not necessarily propor- 
tional to it; regard must be had as well to the 
rainfalls of previous seasons and the “ tail” of the 
flow produced by them.—Gertrud Theiler: Two 
new species of nematodes from the zebra. Cvylindro- 
