JANUARY 25, 1917] 
therefore necessary to employ the substitution of an 
amidic group with a nitroxyl in a convenient dinitro- 
toluidine. Of these latter, three were suitable for lead- 
ing to the necessary transformation. An additional 
result obtained by these authors was the production of 
60 per cent. of one of the dinitrotoluidines, of which 
previously it had been only possible to obtain 20 per 
cent. from the material employed. The paper also 
describes the properties of a considerable number of 
the corresponding dinitrotoluene halogen compounds. 
A paPeR by Dr. S. Brodetsky, on the longitudinal 
initial motion and forced oscillations of a disturbed 
aeroplane, appears in the Aeronautical Journal for 
October-December, 1916 (No. 80). The main conclusion 
is that “‘the ideal aeroplane is one that combines the 
following characteristics ; large velocity, small angle of 
attack, smal] ratio area/load, small tail fairly far 
behind the main plane, and considerable margin of 
stability." The practical man will probably say that 
this is what common sense would predict, but it is 
interesting to see how these conclusions follow mathe- 
matically from a few simple assumptions, and the 
history of modern aviation shows that they have not 
always been acted upon. As in tthe case of a balance, 
the increase of one virtue involves the decrease of 
another, and we have to make a compromise; examples 
of this will be found in the paper, Fortunately 
stability and speed go together, and the disturbing 
elements, in all probabilify, will be gradually 
eliminated in the case of rapid machines. Then will 
come the problem of combining comparatively low 
speed with sufficient stability: a question of design, 
as in the case of a bicycle. Prof. G. H. Bryan has 
contributed an interesting introduction. 
In the Journal of the Franklin Institute for Decem- 
ber last Mr. I. Langmuir describes a new form of 
exhaust pump for the production of high vacua, which 
he proposes to call the ‘‘condensation pump.” It may 
be constructed of metal or of glass. The metal form 
of the pump consists of a tall cylindrical vessel con- 
taining a shallow pool of mercury, which is heated 
electrically and gives off mercury vapour. The up- 
ward stream of vapour is concentrated towards the 
centre of the vessel by an inverted funnel, and on issu- 
ing from the funnel strikes the under surface of a 
bell-shaped deflector, which sends it downwards along 
the outer walls of the upper portion of the containing 
vessel. The space above the bell is in communication 
with the vessel to be exhausted, and the moving mer- 
cury vapour drags along with it the gas from 
this vessel. The outer wall of the containing 
vessel along which the mixture passes is cooled by 
an outer water-jacket, and the mercury vapour is con- 
densed on it, and runs down into the pool at the 
bottom of the vessel. The gas continues its motion, 
and is taken from the lower part of the vessel by an 
auxiliary pump giving a pressure of 200 to 600 bars. 
A pump of this form, 7 cm. in diameter, exhausts 
3000 c.c. of gas per second, and will reduce the pres- 
sure to 10-° bar (1 atmosphere=10° bar). 
A copy of the “ List of Publications of the Carnegie 
Institution of Washington,” issued on December 1 
last, has been received. Copies of each publication, 
except the monthly issues of the ‘Index Medicus,” 
are sent gratuitously to a carefully selected list of the 
greater libraries of the world, while the remainder of 
the edition is offered for sale at a price sufficient only 
to cover the cost of publication and the carriage to 
purchasers. Persons desiring price lists or descriptive 
lists as issued may have them by applying to the 
Carnegie Institution of Washington. The catalogue 
NO. 2465, VoL. 98] 
NATURE 
| normal. 
| 44077 was the first line shown by Adams to be related 
417 
received contains both price and descriptive lists, and 
the latter is a most useful guide to the character and 
precise contents of each of the volumes indexed, so 
that would-be purchasers may know exactly the kind 
of book they are ordering. 
Mr. Leonarp Huxtey, who, it will be remembered, 
was his father’s biographer, has written for early pub- 
lication by Messrs. Smith, Elder and Co. ‘The Life 
and Letters of Sir J. D. Hooker, O.M., G.C.S.I.”—a 
work which is sure to be of interest to very many 
readers of Nature. It will be illustrated by photo- 
gravures and be in two volumes. 
A sEconpD and much enlarged edition in two volumes 
of Mr. A. Marshall’s ‘‘ Explosives: their Manufacture, 
Properties, Tests, and History,” is to be brought out 
by Messrs. J. and A. Churchill. The first volume, 
containing a portrait of the Prime Minister, to whom 
the work is dedicated, will be published almost imme- 
diately. The work as originally published was re- 
viewed in Narure of June 3, 1915, and the author con- 
tributed an additional chapter, under the title of ‘‘ The 
Nature of Explosives,” to our issue of February 3, 
1916. 
OUR ASTRONOMICAL COLUMN. 
Ec.ipsEs OF JUPITER’S SaTELLITES.—In Harvard Cir- 
cular No. 198 Prof. E. C. Pickering directs attention 
to the need for continued observations of the eclipses 
of Jupiter’s satellites. He points out that the observa- 
tions are easy and interesting, and such as can readily 
be undertaken by amateurs. While the probable error 
of a photometric determination of the time of an 
eclipse is about 2 seconds, the average deviation from 
the time computed by the tables of Prof. Sampson is 
about 7 seconds. These deviations appear to be real, 
and a possible explanation is that the apparent 
diameter of the planet, and therefore of its shadow, 
varies with the cloudiness of the Jovian atmosphere. 
Several independent observations tending to confirm 
large deviations from theory would thus be valuable. 
PECULIAR STELLAR SpEcTRA.—In a paper read at the 
nineteenth meeting of the American Astronomical 
Society Miss Cannon directed attention to some of the 
peculiar spectra which had been noted in the prepara- 
tion of the New Draper Catalogue (Popular Astro- 
nomy, vol. xxiv., p. 656). It appears that while less 
than one-fifth of one per cent. of the 218,000 stars 
which have been classified fall outside the classes B, 
A, F, G, K, M, many stars which may be classed in 
these divisions show abnormal features. In all classes 
some stars have been found which show lines of un- 
usual intensity; thus several hundred additional stars 
have been found to show the silicon lines 1.4128 and 
4131, or the strontium line 44077, stronger than 
The latter group.is of special interest, as 
in intensity to the absolute magnitudes of the stars. 
| In C.P.D. —59° 3038, mag. 7-2, a line near A 3869, 
which may be a reversal of a well-known nebular line, 
has been found to be very strong. Real changes in 
the spectra of several stars have also been observed; 
thus in » Carine, as photographed in 189s, the 
hydrogen lines were stronger, and other bright lines 
fainter, than on the more recent plates. An extreme 
case of variation is R. Scuti, which ranges from G5 
at maximum to Mb at minimum. The only new type 
of spectrum which has been found is that exhibited 
by the very red star B.D.+43°-53, the spectrum con- 
sisting entirely of light near the region of Ha, and the 
colour-index amounting to 5-4 magnitudes. This and 
