594 
NAT ORE 
[Aucust 6, 1914 
or in a solid, the molecular groups, which are in 
thermal agitation, have magnetic moments which are 
functions of the temperature. Their action on each 
other is due partly to actual impacts, partly to the 
magnetic field each sets up in its neighbourhood. In 
general the second effect is small compared with the 
first. When an external field is applied, both the im- 
pacts and the molecular fields tend to oppose the 
rotation of the magnetic axes of the molecules or 
molecular groups into line with the field. If the mole- 
cules or groups are elongated in shape the impacts 
almost entirely prevent rotation and the substance is 
paramagnetic. If the molecules or groups are 
spherical the impacts have only a small effect, rotation 
is resisted mainly by the mutual magnetic actions 
and the substance is ferromagnetic. Diamagnetism 
he considers to be atomic in nature and only another 
aspect of the Zeeman effect. 
OUR ASTRONOMICAL COLUMN. 
Comer 1913f (DELAvAN).—The following is the 
ephemeris for Delavan’s comet (1913f) for the current 
week (Astronomische Nachrichten, No. 4739) :— 
; R.A. (true) Dec. (true) Mag. 
° m. Ss. ° ‘ “ 
ANUS, Gs Sys. Ow 21 EO . +40 40 17:9 
fa ee 2H AGS ocel, IMEL FON Aye] «| =e ROLE 
Saree 2815356) .. 4 2Dy20°0 
2) coc BE DAE” eas ete oad, 
HOiMMess Be BRa 1 ts ee la2 228-0 
ni BOZO | wactomig2 23 MaeO sy jctacar 59 
Tein ees AGINS-2 = A Nee Aaa. Sans 
na ere 4elG-O - +43 4 46 
The current number of the Observatory (August) 
states that this comet was detected by Mr. W. H. 
Steavenson on July 4 at an altitude of 1°. It was of 
about the 6th magnitude, had a nucleus of magnitude 
7-5, and a head of five minutes in diameter; daylight 
prevented the tail from being observed. It is expected 
that the object will be visible to the naked eye in 
September and October, but no more confident pre- 
diction than this can now be made. 
NEBULAR Roration.—In this column on June 4 
(vol. xciii., p. 361) reference was made to an announce- 
ment by Prof. Lowell of the discovery, by spectroscopic 
means, of the rotation of the Virgo Nebula. Dr. 
V. M. Slipher now publishes (Lowell Observatory 
Bulletin, No. 62) a brief communication describing 
in more detail the discovery in question. It seems 
that about a year ago a spectrogram of the Virgo 
Nebula N.G.C. 4594 showed the nebula lines to be 
inclined. A second plate verified the above, but was 
not considered sufficiently satisfactory to warrant a 
public announcement of the discovery. A_ recent 
photograph confirms the previous deduction, and it is 
stated that the inclination of the lines, which is ana- 
logous to that produced by the diurnal rotation of a 
planet, ‘‘is unmistakable, and leads one directly to 
the conclusion that the nebula is rotating about an 
axis.’ This nebula has a radial velocity of fully a 
thousand kilometres a second. The nebula is of a 
‘‘spindle’’ type, and the slit of the spectroscope was 
placed over the long axis: these nebulz are thus 
spirals seen edgewise, as previous observations of 
their form have led one to believe. The fact is now 
proved. Dr. Slipher promises the details of the ob- 
servations in a general discussion of the spectro- 
NO; 239G VOU, 193i ; 
graphic observations of nebula made since i912. 
Some of the numerous spectrograms of nebule taken 
at Flagstaff have shown indications of inclined lines, 
among them being the great nebula in Andromeda, 
and he hopes to give a definite answer to the im- 
portant question of the rotation of this the greatest 
of spiral nebulz. 
SoLarR PHysicS OBSERVATORY, CAMBRIDGE.— lhe first ° 
annual report of the director of the Solar Physics 
Observatory, Cambridge, to the Solar Physics Com- 
mittee covers the year commencing April 1, 1913. 
The introductory remarks contain a statement indicat- 
ing the circumstances in which the observatory is now 
administered, and deplore the loss of three members 
et the committee, namely, Sir George Darwin, Sir 
Robert Ball, and Sir David Gill, since the appointment 
of the committee in June, 1912. After a reference to 
the purchase of additional land extending down to the 
Madingley Road and to the selection of instruments 
to be used, the new buildings are next described. 
These include an extensive and complete laboratory 
building forming an extension at the west end of the 
astrophysical building, a spectroheliograph house, a 
dome 27 ft. in diameter for the 3-ft. reflector, etc. The 
energies of the staff are stated to have been chiefly 
confined to getting the observatory into working order, 
and for this reason systematic work not involving 
fresh observations was undertaken, and night work 
put somewhat in abeyance. Under the heading 
“Stellar Work,”’ the photographic and visual observa- 
tions made with the Newall telescope are recorded. 
These consist of spectrograms of variable stars and 
visual observations of the spectra of fine nove. A 
discussion of spectrograms of Nova Persei No. 2 has 
been completed, and an atlas of typical stellar spectra 
with assigned chemical origins of the lines is in 
course of preparation. | Under the heading, ‘Solar 
Work,” that with the spectroheliograph and _ the 
McClean solar instruments is dealt with, while in 
meteorological physics a brief account is given of the 
investigations in atmospheric electricity and experi- 
mental work on ionising radiations. Preparations 
were made for the observations of the coming eclipse 
of the sun, the director and two members of the staff 
planning to take up their station near Feodosia in the 
Crimea. 
ANNALS OF THE RoyaL BELGIUM OBSERVATORY.—The 
second part of vol. xiii. of the Annals of the Royal 
Observatory of Belgium contains three separate 
memoirs. The first is confined to the details of ob- 
servations of variable stars made at that observatory 
during the period 1907 to 1912 by Messrs. G. van 
Biesbroeck and L. Casteels. Forty-six stars are here 
studied and the total number of observations published 
is 3225. Chief attention has been paid to new vari- 
ables which have not been ‘well studied. In many 
cases their identity was so ambiguous that the authors 
have studied the stars themselves, and for the sake 
of future observers have published charts of the regions 
where those stars were not included in the Bonner 
Durchmusterung. In many cases light curves accom- 
pany the text. The second portion of the volume 
brings together the observations made with the 
38 cm. aperture equatorial by Dr. G. van Biesbroeck 
during the period 1907 to 1912; these comprise the 
observations of double stars, comets, minor planets, 
and phenomena. The third and last portion, by 
M. L. Casteels, summarises the physical observations 
of comets made by him in the years 1910 and IgII. 
Both the second and third portions are accompanied 
by numerous illustrations of the details observed in 
comets’ heads. 
