’ 

+ 
a 
_ after each opposition. 
May 26, 1923] 
NATURE 
717 

Institut, Christiania; Prof. T,G. Halle, Naturhistorisk 
Riksmuseum, Stockholm ; Prof. J. F. Kemp, Columbia 
University, New York City; Prof. C. F. Kolderup, 
University of Bergen; Prof. C. I. Lisson, Escuela de 
Ingenieros, Lima; Prof. G. A. F. Molengraaff, Delft ; 
Dr. A. Rénier, Directeur du Service Géologique de 
Belgique; Prof. P. Termier, Directeur des Services de 
la Carte Géologique de France; and Dr. F. E. Wright, 
Geophysical Laboratory, Washington, D.C. 
Tue floral ballet, composed by Dr. G. Rudorf, and 
conducted by him at the Alexandra Palace on May 19, 
in aid of the Royal Northern Hospital, as announced 
in last week’s issue, p. 681, proved very delightful 
music. Specially written for a choreographic flower- 
story arranged by Mrs. A. E. Ormen Sperring for her 
pupils, the work, which lasted three-quarters of an 
hour, contains a great variety of melodic material. 
In his professional capacity as a chemist, and as 
collaborator with Sir William Ramsay in a treatise 
on the rare gases, Dr. Rudorf is well known; and 
he is to be congratulated upon the skill he has 
shown in the production of a musical work of real 
merit. 
Mr. F. Epwarps, 83 High Street, Marylebone, W.1, 
has just circulated a catalogue (No. 443) of some 
I1r0o books and serials relating to anthropology, 
folklore, archzology, etc., some of which formerly 
belonged to Prof. Huxley. We notice that Mr. 
Edwards has also for disposal a small collection of 
Australian native weapons and implements of the 
period 1840-50, from the collection of Mr. S. T. Gill, 
an Australian artist. 
Our Astronomical Column. 
THE THEORY OF JUPITER'S SATELLITES.—Prof. de 
Sitter, of Levden, lecturing on this subject at the 
_ University of Manchester on May 9, emphasised the 
_ interest attaching to the theory 
of the motion of 
the four Galilean satellites (to which his remarks 
were confined), because they illustrate the more 
important features in the theory of the motion of 
the planets round the sun, but with a time-scale 
reduced in a ratio of about 3000 to 1. The theory 
can thus be checked by observations extending over 
a period of a few decades, but the difficulty of deriving 
from the observations the masses of the satellites, 
and the elements of their orbits, is greatly enhanced 
by the intercommensurability of the periods of the 
three inner satellites. Though the tables published 
by Prof. Sampson a few years ago represented a 
great advance at the time of their appearance, they 
still require to be confirmed and extended by other 
methods. The commensurability of the periods 
tenders the ordinary expressions found in celestial 
mechanics too slowly convergent, and necessitates 
the search for a new solution, starting from a periodic 
solution as the first approximation. The commensur- 
ability also makes the observations of eclipses and 
transits of the satellites less satisfactory than usual 
for the determination of the elements of the system. 
In order to counter these difficulties, such observa- 
tions have to be extended over a whole period of 
revolution of Jupiter (12 years) and supplemented 
by photographs taken at selected epochs before and 
Such observations have been 
made at Greenwich, the Cape, and Johannesburg, 
and are now in Prof. de Sitter’s hands for discussion. 
The discussion is well in hand, and the results promise 
to be satisfactory. 
Unknown LINES IN STELLAR SPEcTRA.—To all 
spectrosco ists the paper by Mr. F. E. Baxandall on 
“Lines of Unknown Origin in various Celestial 
Spectra ”’ (Mon. Not. R.A.S., vol. 83, p. 166) will be 
very welcome. Mr, Baxandall’s skill in deciphering 
spectra is well known, so the results here collected 
are of special value. In the year 1910 Sir Norman 
Lockyer published a list of fairly prominent lines for 
which no satisfactory origins had been found, but 
since then many of them have been run to earth, 
notably the line at \ 4688, which is now known to 
be due to ionised helium, and the ¢ Puppis lines due 
to the same element. Eliminating these lines from 
the list of unknowns, Mr. Baxandall gives rather a 
NO. 2795, VOL. 111] 
formidable table containing about 130 lines still 
unknown. The wave-lengths of these lines have all 
been observed in some source of celestial light, and 
the table indicates which particular source, whether 
sun, star, corona, nebula, and so on, in which they 
have been observed. The paper is accompanied by 
copious notes and references. 
850 New Nesuta.—Dr. Harlow Shapley, in the 
Harvard College Observatory Bulletin, No. 784, points 
out that photographs made with the Bruce telescope 
at Arequipa, Peru, supplement the data for nebule 
not easily reached from northern observatories. On 
a photograph made on September 19, 1922, with an 
exposure of six hours, centred on R.A. 22" 40", 
Dec. — 45°, Dr. Shapley has found 850 new nebule. 
On the following night another exposure was made, 
this time for two hours only, which showed all objects 
brighter than the eighteenth magnitude. He points 
out that these new nebulz are not of the nature of the 
faint irregular nebulous wisps frequently found in the 
vicinity of bright spirals, but are distinct nebule, the 
fainter ones almost exclusively oval or circular in 
form, distributed over an area of about thirty square 
degrees. It is interesting to note that only three 
nebule of the N.G.C. fall within this region and three 
from the second Index Catalogue. The brighter 
nebule are, almost without exception, elongated or 
show spiral structure, while the fainter ones appear 
largely to be globular. The shape of these latter, as 
Dr. Shapley points out, may be due simply to under- 
exposure of the plate, since many of the bright 
nebulz, on a short exposure, lose the faint extensions 
that reveal their truly elongated shape. The inter- 
esting remark is made that on many parts of this plate 
at the eighteenth magnitude, the nebule are more 
numerous than the stars. 
THE ASTRONOMICAL SOCIETY OF SOUTH AFRICA.— 
A local astronomical society was formed at Capetown 
ten years ago; this has now been extended to include 
the Johannesburg society, and the first Journal of the 
combined body was published in February. The 
inaugural presidential address by Dr. Hough deals 
with the tides in a clear and interesting manner, 
explaining methods of tidal analysis and prediction, 
and giving an outline of Sir G. Darwin’s theory of the 
development of the earth-moon system by tidal 
evolution. The society has been especially active 
in comet and variable star work ; the former is fully 
dealt with in the Journal. 
