| 
| | 
_ the slightest inequality in temperature. 
_ produced by hand. 
_ placed on a 2-inch diameter wooden 
Sept. 9, 1886] 
NATURE 
463 
See 
In other words, the electromotive force in a circuit of palladium 
and saturated hydrogenium,’ the temperatures of the junctions 
being 0° C. and 100° C., is 20 X 10 C.G.S. units, or ‘002 volts. 
The thermo-electric peculiarities of hydrogenium may be prettily 
shown by the following simple experiment. Let a palladium 
wire, by immersion to half its length in the electrolytic cell, be 
hydrogenised throughout that half length. Attach the ends of 
this seeming single uniform wire to the terminals of a galvano- 
meter, and let a flame be allowed to play gently at the central 
point of the wire. A large current is at once obtained, which 
grows to a maximum, and then diminishes to zero as the tem- 
perature rises toa red heat. There is no such current during 
cooling. This spurious neutral point is due to the hydrogen 
being driven out of the heated portion, partly, no doubt, into 
the contiguous colder portions. By following up with the flame 
the ever-shifting point of separation between the charged and 
uncharged portions, we may repeat the experiment indefinitely 
until the hydrogen is all driven out of the wire, or until the 
distribution of hydrogen has become fairly uniform,—Mr. 
Thomas Andrews communicated a paper on the electro-chemical 
reactions between metals and fused salts.—Mr. H. N. Dickson 
communicated a paper on the hygrometry of Ben Nevis and the 
Scottish Marine Station.—Mr, J. T. Morrison read a paper on 
the temperature of Loch Lomond and Loch Katrine during 
winter and spring ; also, a note on the surface temperature near 
a tidal race.—Mr. John Aitken gave further remarks on dew.— 
Prof. J. B. Haycraft gave a communication on the nature of the 
objective cause of sensation. 
SYDNEY 
Royal Society of New South Wales, July 7.—H. C. 
Russell, F.R.A.S., in the chair.—The following papers were 
read :—Further additions to the census of the genera of plants 
hitherto known as indigenous to Australia, by Baron Ferd. von 
Miiller, K.C.M.G., F.R.S. The author gives the number of 
Australian plant-genera recorded hitherto as 2248.—Notes on 
improvements in the construction of reflecting telescopes by 
hand, and experiments with flat surfaces, by Mr. H. F. Madsen. 
The author showed an 18-inch speculum, and the glass tool 
with which it wasworked. The latter was composed of three 
plates of 1-inch rough glass cemented to form a solid block, and 
worked to about one-quarter more convexity than the required 
concavity of the speculum, which was partly hollowed out at first 
by a leaden weight and emery. The speculum-glass was then 
ground by hand over the block, the two forming themselves into 
perfectly spherical surfaces having a high reflective power, and 
free from irregularities of less than 1/50,000 inch. ‘The specu- 
lum, having now an absolutely true surface, was polished with 
emery upon pitch, it being uppermost, and moved round with- 
out pressure. The pitch-polisher had an improved graduation, 
the result being that, without side motion, the speculum was 
polished by hand for hours without producing the trace of a 
ring. Both polisher and glass having been regularly raised in 
temperature, were left together until cool, when ten minutes was 
required to give the true parabolic curve, the glass being simply 
revolved on the polisher, great care being taken to avoid 
Without the aid of 
machinery, it is doubtful if larger specula than 18-inch could be 
Mr. Madsen investigated the thickness of 
the silver film of a speculum by a novel optical method, and 
confirmed the late Dr, Draper’s ‘‘chemical” estimate, viz. 
-1/200,000 inch. Two perfectly flat surfaces 5 inches diameter 
were taken and illuminated by a homogeneous yellow light of 
1/44,000 wave-length, falling at an angle of 30° incidence 
(Brashear’s colour-test), whereby a series of straight dark and 
_ coloured bands were visible. By silvering half the upper surface 
of one of these glasses the bands were displaced or broken at 
the edge, a distance of about 2 (x being the distance between 
two succeeding bands). The thickness of silver, 5, would be 
expressed by 
A (wave-length) 
5 
Several measurements gave less than 1/300,000 inch. Under 
the same optical methods the effects of heat and cold were ren- 
dered plainly visible and measurable. The true surfaces were 
chuck ; the light falling at 
On applying the finger without 
sec 30 = 0°c0000525,. 
65° gave a uniform colour. 
~ pressure upon the centre of the top glass, the colour changed to 
reguiar concentric rings, causing the glass to become concave by 
a measurable quantity. Placing the glass upon an iron support 
produced convexity (1/30,000 inch) ina regular curve. With a 
pressure of 8 lbs. on the centre, two wide bands of colour ap- 
peared, crossing in the centre, straining the glass in two direc- 
tions, and destroying its figure. These experiments show how 
the defining power of specula and lenses is injured by tempera- 
ture. 
Paris 
Academy of Sciences, August 30.—M. Emile Blanchard in 
the chair.—In the name of the Academy the President felicitated 
M. Chevreul on his hundredth anniversary, remarking that the 
case was unique in the annals of the Academy ; even Fontenelle, 
although spoken of as a centenarian, having died shortly before 
reaching that venerable age. M. Chevreul replied with a few 
touching words of gratitude for the sympathy of his confréres, 
after which a telegram was read from the University of Kasan 
complimenting the patriarch of the scientific world on his long 
and laborious life, so fruitful in valuable contributions to the 
progress of the technical arts.—On a remarkable case in the 
problem of planetary perturbations, by M. F. Tisserand. In 
the case of two planets revolving round the sun, or of two satel- 
lites round their planet, in orbits slightly inclined towards each 
other, it is shown that even if the proper excentricity be null 
there may be a very sensible apparent excentricity. In other 
words, if the movement of one orb was originally circular and 
uniform, the perturbations caused by the other would transform 
this movement into one approximating to a Keplerian elliptical 
orbit with a uniform rotation of the long axis. These results 
are compared with those obtained by A. Hall and S. Newcomb 
for the Saturnian satellite Hyperion, in so far as its movement 
results from the perturbations caused by the larger satellite 
Titan. —On the atomic weight of germanium, by M. Lecoq de 
Boisbaudran. The atomic weight of this body, provisionally 
determined by M. Winkler at 72°75, and by the author theo- 
retically at 72°28, is now found by M. Winkler to be 72°32. 
The law of proportionality between the variations of the atomic 
weight and those of the waye-lengths, a law already applied to 
gallium, here receives a fresh and important confirmation. It 
becomes at the same time highly probable that no appreciable 
error now exists regarding the atomic weights of caesium, rubi- 
dium, potassium, indium, gallium, aluminium, tin, and silicium. 
In fact the wave-lengths and atomic weights of Cs, Rb, K, In, 
and Al have served to calculate spectrally the atomic weight of 
gallium (afterwards verified analytically), while the A and atomic 
weights of In, Ga, Al, Sn, and Si have helped to determine 
spectrally the atomic weight of germanium.—Note on a reptile 
of the Permian formation, by M. Albert Gaudry. To this 
reptile, which was found by M. Bayle in the Permian 
beds of Télots, near Antun, the author proposes to give 
the name of Haftodus baylei (from értw and ddovs), the teeth 
adhering so closely to the maxillaries as at first sight to be 
scarcely distinguishable from them. In these rocks, where no 
animals higher than fishes were for a long time known to occur, 
there are now found four distinct types of Reptilia: Actinodon, 
Protriton, Stercorachis, and Haptodus.—Phosphorography ap- 
plied to the photography of the invisible, by M. Ch. V. Zenger. 
Observing Mont Blanc after sunset in September 1883, the 
author noticed that the blue-greenish glow\remained perceptible 
till 10.30 p.m. ; hence he concluded that the ice on the summit 
mingled with carbonate of lime emitted a light like that of Lake 
Geneva, and that it might be possible to fix the image of the 
mountain at night by means of the phosphorescent light of the 
ice, which is highly actinic. On his return he projected the 
images given by the photographic lenses in the dark chamber on 
a glass plate covered with a layer of Balmain’s phosphorus, just 
as such plates are prepared with collodion. After exposing it 
for a few seconds, he removed it in the dark from the chamber 
in order to place it in contact with a not very sensitive dry 
photographic plate. After an hour of contact in the dark, the 
image of the object appeared in all its details as in an ordinary 
case of photographic impression. Subsequent experiments 
tended to show that light may be absorbed, and afterwards 
slowly given back, and that images of objects invisible in the 
dark may be fixed by simple contact, or by the photographic 
apparatus. He found it useful to cover the plates with chloro- 
phyll, as when thus prepared they become sensitive to all the 
radiations of the solar spectrum from the ultra-red to the ultra- 
violet.—Observations of Winnecke’s comet made at the Obser- 
