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FEBRUARY 25, 1897 | 
NATURE 
401 
men of science in the United States. The Institution has 
renewed for three years the lease of the Smithsonian table at the 
Naples Zoological Station. The table has been constantly 
occupied since October 1, 1893, the date of the first appoint- 
ment, with the exception of May 1894. During the intervals of 
his official duties, Prof. Langley has continued to experiment 
with the aérodrome, until he has reached a measure of success 
which, he announces, justifies him in making the statement that 
mechanical flight has now been attained. On May 6 last, a 
mechanism, built chiefly of steel and driven by a steam engine, 
made two flights, each of over half a mile (see NATURE, vol. liv. 
p- 80). Since then Prof. Langley says this result has been 
doubled. In the astrophysical observatory Prof. Langley has 
continued his researches upon the solar spectrum. The results 
of the year’s work are summed up by the statement that an 
entirely new stage of accuracy has been reached by the 
elimination of sources of error, of long standing, in the spectro- 
bolometric processes, and that as a result of this accuracy it is 
expected that the positions of between 200 and 300 lines in the 
infra-red spectrum will shortly be published. 
By his further investigation of the reversible decomposition of 
hydriodic acid gas, published in the February number of the 
Zeitschrift fir phystkalische Chemie, Mr. Max Bodenstein 
removes all doubt as to the normal character of this change, 
thus adding another to the very small number of reactions 
between gases which are known to follow the laws of mass 
action. Ina former investigation he had found that, at a given 
temperature, the fraction of the hydriodic acid decomposed 
when equilibrium was attained was not independent of the 
pressure of the gas. Since the decomposition takes place with- 
out change of volume, theory indicates that, at constant tem- 
perature, the equilibrium should be unaffected by a change 
of pressure. This discrepancy is removed by the experiments 
described in the present paper. Known quantities of hydrogen 
and iodine are heated in sealed glass bulbs at a constant tem- 
perature until equilibrium is attained, whereupon the quantities 
of hydrogen, iodine, and hydriodic acid present are determined. 
This leads to the, at first sight, somewhat surprising result that 
equivalent quantities of hydrogen and iodine have disappeared. 
In one experiment neither hydriodic acid nor iodine were found 
in the heated bulb, the whole of the iodine used having dis- 
appeared. The cause of this loss is found in the combination 
of hydriodic acid with the glass ; part of the iodine is found as 
sodium iodide; the greater part, however, appears to form some 
compound insoluble in water. When the diminution in the 
concentration of the hydriodic acid gas, to which the combina- 
tion of part of it with the glass gives rise, is taken into account, 
it is found, in accordance with theory, that the fraction of the 
hydriodic acid decomposed, at constant temperature, when 
equilibrium has been reached, is independent of the pressure. 
IN a second paper, on the decomposition of hydriodic acid 
gas by sunlight, it is found that on prolonged exposure the 
whole of the hydriodic acid is decomposed ; the change is thus 
not reversible. The intensity of the light remaining constant, 
the quantity decomposed in unit time is simply proportional to 
the quantity of undecomposed hydriodic acid present, and is 
not affected by its pressure (within the limits 0°5 and 1 atmo- 
sphere approximately). These are the characteristics of a mono- 
molecular reaction, and it therefore follows that each molecule 
of hydriodic acid is decomposed independently, each ray of 
light, of proper vibration frequency, simply breaking up the 
hydriodic acid molecules in its path. 
THE addition to the Zoological Society’s Gardens during the 
past week include a Green Monkey (Cercopithecus callitrichus, 6 ) 
NO. 1426, VOL. 55] 
from West Africa, presented by Mr. John Laxson; a Rhesus 
Monkey (Macacws rhesus, ?) from India, presented by Mr. W. 
H. Camm; a Grey Lemur (Hapalemur griseus) from Mada- 
gascar, presented by Mr. W. B. Dyer; a Greater Vasa Parrot 
(Coracopsis vasa) from Madagascar, presented by Surgeon Lieut. - 
Colonel F. H. Gelbresa ; an Upland Goose (Ch/oephaga magel- 
fanica, 8) from the Falkland Islands, deposited ; five Azara’s 
Opossums (Déidelphys azare), ten Burrowing Owls (Speotyto 
cunzcularza) from South America, eight Guira Cuckoos (Guzra 
Pirtrigua) from Para, two Uvean Parrakeets (Mymphicus 
wveenses) from the Island of Uvea, Loyalty Group, a Smew 
(Mergus albellus, 9) from Holland, purchased. 
OUR ASTRONOMICAL COLUMN. 
PERIODICAL COMETS.—The present year seems to be some- 
what barren of appearances of periodical comets, while, on the 
other hand, the two following years will be distinguished by the 
returns of several well-known comets. 
This year’s visitors are limited to three altogether, namely, 
1890 VII., D’Arrest’s, and Swift’s. The first named seems, from 
all accounts (Oéservatory, No. 249), to be most probably very 
feeble in intensity, since at its appearance in 1890 it was an 
excessively faint object. The comet was described by Dr. 
Spitaler at Vienna, and a computation showed that it had a 
period of 6°4 years, so that it should make its perihelion passage 
on March 11. Those who wish to search for this comet will 
find an ephemeris in Ast. Wach., No. 3370. 
D’Arrest’s comet, discovered at Leipsic in June of the year 
1851, has also a period of nearly the same length, namely, 6°5 
years. This comet has not been observed at every period, 
having been seen only in the years 1857, 1870, 1877, 1890. It 
is probable that even this year it will be missed, in consequence 
of its unfavourable position. A daily search’ ephemeris (March 
to August) for this year will be found to be given by M. G. 
Leveau in the Bzdlete Astronomigue for last month (January). 
Swift’s comet will not be seen, owing to the fact that it will 
be lost in the sun’s rays, as the earth will be in the opposite 
part of her orbit to that nearest the comet at perihelion passage. 
Acomet that may be picked up again this year is Brooks’ 
1886 IV., and observations of this comet are wanted, as the 
period is not yet accurately determined. 
A list of the comets which are due to appear in the next two 
years is quite a formidable one, as given by Mr, W. F. Denning 
in the current number of the Odservatory :— 
1898. Comet. 1899. Comet. 
April Pons-Winnecke. Jan. Denning (1881 V.). 
May Encke. Mar. Tempel (1886 I.). 
June Swift (1889 VI.). April Barnard (1892 V.). 
June Wolf. May Tuttle (1858 I.). 
Sept. Tempel (1867 II.). | May Holmes(1892 IIT ). 
July Tempel (1873 II.). 
OBSERVATIONS OF Mars at Mreupon.—M. Perrotin, whose 
observations of Mars are very well known, commenced at Meudon, 
in December of last year, a series of observations of that planet. 
The instrument he used had a diameter of 0°83 metres, and he 
has been able to make some very interesting observations, which 
have been communicated to the Comptes vendus for February 
15. Acareful survey of the planet has led him to state that 
the disc is apparently divided, as regards general aspect and 
colour, into four zones lying parallel to the equator. Two of 
these comprise the equatorial regions. Further, he has noticed 
that at equal distances from the centre of the disc the surface 
details do not appear with equal facility in the four zones. The 
canals are always most distinct towards the middle of the disc, 
and they are visible for a further distance along a meridian than 
along a parallel. M. Janssen remarks, with regard to the latter 
point, that the observations show that the atmosphere of Mars 
contains bodies capable of condensing, and thereby of increasing 
the transparency of the atmosphere, as the polar regions are 
approached, which is in accordance with observations of the 
water vapour in the atmosphere of the earth. We may mention 
that the above observations are of special interest, since M. 
Perrotin is observing with a different instrument from that with 
which he has made all his previous observations. 
