518 
NATURE 
[ Marcu 28, 1907 
in science and industry; Sir Harry Johnston’s paper to 
the Royal Geographical Societv, on Liberia; as well as 
other contributions by British workers in science. The 
fine illustrations add greatly to the interest of the volume. 
A THIRD edition of ‘‘A Text-book of Plant Diseases 
caused by Cryptogamic Parasites,’’ by Mr. George Massee, 
Principal assistant in the department dealing with crypto- 
gams of the Royal Herbarium, Kew, has been published 
by Messrs. Duckworth and Co. 
Vou. iv. of the Proceedings of the London Mathematical 
Society, second series, is now available. The volume is 
published by Mr. Francis Hodgson. Among its contents 
may be mentioned the records of proceedings at meetings 
of the society; obituary notices of the late Astronomer 
Royal of Ireland, Mr. C. J. Joly, F.R.S., and the late 
Mr. Robert Rawson, sometime headmaster of the Dock- 
yard School, Portsmouth; papers published in the Proceed- 
ings from November, 1905, to November, 1906; and several 
useful indexes. Abstracts of papers brought before the 
society appear regularly among our reports of scientific 
societies and academies, 
OUR ASTRONOMICAL COLUMN. 
ASTRONOMICAL OCCURRENCES IN APRIL :— 
April 3. 5h. 48m. to 8h. 55m. Transit of Jupiter’s Sat, III. 
(Ganymede). 
7- 16h. 18m. to 17h. Im. Moon occults + Capricorni 
(mag. 3°8) 
Io. gh. 55m. to 13h. 2m. Transit of Jupiter's Sat. IIT. 
(Ganymede). 
13. Ith. om. Vesta in conjunction with the Moon 
(Vesta 0° 24’N.). 
>», I2h,om. Minimum of Algol (8 Persei). 
14. 16h. om. Mercury at greatest elongation (27° 36’ W.). 
16. 8h. 49m. Minimum of Algol (6 Persei). 
18. 6h. 57m. Jupiter in conjunction with the Moon. 
20-22. Epoch of Lyrid  meteor-shower, Radiant 
271° + 33°. 
21. 2h. 41m. Venus and Saturn in conjunction (Venus 
o° 38’ N.). 
»» Venus. Illuminated portion of disc =0°773. 
30. 15h. 38m. to 16h. 50m. Moon occults ¢ Ophiuchi 
(mag. 4°5). 
Comet 1907a (G1acopin1).—No further observations of 
this comet have yet been received, but the elements and 
daily ephemeris computed by Herr M. Ebell appear in 
No. 4161 of the Astronomische Nachrichten (March 13), 
the latter extending to March 31. An extract is given 
below :— 
Ephemeris 12h. (M.T. Berlin). 
1907 a (‘rue) 6 (true) leg 7 log 4 Bright- 
h. m. . ; ness 
March 27 ... 6 27°4... —3 34°3 -.. O°311Q ... 0°2474 ... 0°67 
29...6 24°9.. —2 164 
31....6 22°7 ... —F 2°3 ... 073122 ... 0°2682 ... 0°61 
_OBSERVATION OF ComMET 1905 1V.—A telegram from the 
Kiel Centralstelle announces a further observation of 
comet 1905 IV. by Dr. Kopff at the Kénigstuhl Observ- 
atory on March 21. The position of the comet at 
1gh. 45-8m. (K6nigstuhl M.T.) was 
R.A.=14h. 58-6m., dec.=21° 18’ S 
and the magnitude was estimated to be 13-8. 
The above position lies in the constellation Libra, and is 
above the horizon from about 11 p.m. to 6 a.m. 
This comet was first discovered, as 1906b, by Dr. Kopff 
at Heidelberg on March 3, 1906, and was observed until 
June, 1906; the perihelion passage occurred on October 18, 
1905. The orbit is remarkable for its great perihelion 
distance (3-3 R.), which has only been exceeded by that 
NO. 1952, VOL. 75] 
of the comet of 1729. The motion is probably parabolic, 
although an elliptic orbit, having a period of 1153 years, 
has been suggested. 
STANDARD STELLAR MaGnitupEs.—In order that astro- 
nomers may have a ready means of reducing their magni- 
tude observations to a uniform scale, Prof. Pickering pub- 
lishes, in Circular No. 125 of the Harvard College Observ- 
atory, the positions and carefully determined photometric 
magnitudes of a selected sequence of stars in the region 
of the North Pole. To determine the magnitudes of other 
stars the following method is suggested :—Two photographs 
are taken, one of the polar region, the other of the region 
to be investigated, and on the former the standard stars, 
on the latter the stars the magnitudes of which are to be 
determined, are marked. Then on a night when the 
atmospheric conditions are good and constant, and at a 
time when the second region is at about the same altitude 
as the pole, a third plate is successively exposed for exactly 
the same time on each of the two regions. 
Thus on the third plate the observer has the standard 
and unknown star-images on the same plate taken under 
exactly the same conditions, and may recognise them by 
superposing, in turn, the two negatives first secured and 
marking off the required images. ‘These may then be 
compared for magnitude, and the results reduced to a 
standard scale by means of Prof. Pickering’s standard list. 
Tue SpectRuUM AND RapiAL Vetocity or Mrra.—In 
No. 1, vol. i., of the Journal of the Royal Astronomical 
Society of Canada, Mr. J. S. Plaskett, of the Dominion 
Observatory, publishes the results of a spectrographic in- 
vestigation of Mira during the most recent maximum. 
The spectra were obtained with a three-prism Brashear 
universal spectroscope giving a linear dispersion at Hy 
of 18-6 tenth-metres per millimetre, and having a_ re- 
solving power of 40,000. The results obtained by measur- 
ing two plates are in good agreement with one another 
and with the results obtained by Prof. Campbell and Mr. 
Stebbins. For the absorption lines a radial velocity of 
+65-6 km., reduced to the sun, was obtained, and as 
this is practically the value obtained by the other two 
observers mentioned, in 1897 and 1902, it appears that the 
receding motion of Mira in the line of sight is constant. 
The velocity, as determined from the bright hydrogen 
lines, is some 15 km. less, and Mr. Plaskett suggests that 
this difference is probably due to some abnormal con- 
ditions of pressure, temperature, or electrical state in the 
atmosphere of the star. 
The present spectrograms show that titanium is un- 
doubtedly represented in the spectrum of Mira, a point 
considered doubtful by Stebbins in 1902, and that the 
magnesium line at A 4571, bright in 1902, is now repre- 
sented by a normal absorption line; Hf is fairly strong 
as a bright line, but He cannot be seen on these spectra. 
Two RapipLy-CHANGING VARIABLE StTars.—In No. 5 of 
the Comptes rendus M. J. Baillaud announced the dis- 
covery of two new variable stars of which the light changes 
were so rapid as to be shown on plates taken at the Paris 
Observatory with three successive exposures at intervals 
of half an hour. During the period of observation one of 
these stars changed from magnitude 14-5 to magnitude 
12-7; the other changed from 14-5 to 13-6. As there are 
not likely to be many photographic images of these faint 
objects, they have been looked for on the Harvard photo- 
graphs, and in Circular No. 126 Prof. Pickering publishes 
the information that has been gathered from thirteen 
plates. 
A New AstRonomicaL JouRNAL.—We are pleased to be 
able to record that, with an increased grant from the 
Dominion Government, the Royal Astronomical Society of 
Canada has commenced the publication of a bi-monthly 
journal recording the proceedings of the society. The first 
number (January and February, 1907) contains inform- 
ation regarding the society and several very interesting 
papers. Among the latter may be mentioned two papers 
by Mr. Stupart on magnetic storms and aurora, the presi- 
dent's address on the astronomical work of 1906, and a 
paper by Mr. Plaskett on the spectrum of Mira, referred 
to above. 
