

ee” 
AUGUST 12, 1915] 

NATURE 
655 

by making the mean brightness of white (Ao) stars 
near the sixth magnitude equal to the mean of their 
visual magnitudes in Harvard Circular 170. 
The photovisual scale was obtained in precisely the 
same manner, isochromatic plates being employed. 
Final photovisual magnitudes were obtained for 339 
stars between magnitudes 2-1 and 17-5. About 300 
stars are common to both lists, and for these colour 
indices are consequently available; for the bright stars 
this is small, or even negative, at the seventeenth 
photovisual magnitude the smallest value is 0-6 or 0-7. 
That the faint stars are all relatively red is thus 
confirmed. 
METEOROLOGY OF THE Sun.—Aj lecture delivered 
before the Royal Meteorological Society last March 
by Prof. W. G. Duffield is reported in full in the 
Quarterly Journal of the Society. Whilst, of course, 
primarily adapted to the needs of meteorologists, it 
is too valuable an essay on the present position of 
solar research to be neglected by anyone interested 
in such work. The subject was divided into a 
number of sections; one of these, dealing with the 
pressure in the sun’s atmosphere, has special interest 
in consequence of Prof. Duffield’s own work on the 
effects of pressure on spectra. Electrical conditions 
in the sun’s atmosphere are considered in another 
section, containing the interesting suggestion that the 
“facular masses’? shown on spectroheliograms owe 
their luminosity to a continuous display of lightning 
between their several parts, or to a bombardment by 
negative electrons. Prof. Duffield also suggests that 
solar rotation is the cause of sun-spots and filaments, 
his theory being that the differential velocities of the 
various layers of the solar atmosphere set up vortices ; 
these seen end-on are sun-spots, when floating 
lengthwise appear as filaments. Although neither of 
these ideas is entirely novel, yet both go a little 
further than their precursors. 
The paper is illustrated by a number of useful 
diagrams, and contains reproductions of some fine 
spectroheliograms. 
VARIABLE STars.—Two papers dealing with inves- 
tigations carried on at Princeton Observatory appear 
in the Proceedings of the American Philosophical 
Society, No. 216. In one of these Dr. Dugan (p. 54) 
gives some recent results obtained in the case of the 
eclipsing variables RT Persei and =z Draconis, both 
cases where the light curves have demonstrated ellip- 
ticity of figure, exchange of radiation, and possibly 
darkening at the limb. For RT Persei the shape of 
the light curve possibly indicates that the advancing 
side of the brighter component is brighter than the 
following. Some recent observations of the secondary 
minima show that the eclipses are now coming forty 
minutes earlier than the times predicted from the 
original elements derived from observations taken 
about seven years ago. Extending the period of 
observation by data from Harvard results in a reduc- 
tion of the average period by one second. Using 
this shorter period the residuals reveal two periodic 
terms, the shorter of which closes in about 
4000 eclipse periods, i.e. about nine years, and 
with a coefficient of five minutes. This is of the 
order of magnitude of that to be expected from 
the revolution of the line of apsides caused by the 
observed prolateness. Necessary additional observa- 
tions are being undertaken. Similar results have 
been obtained for z Draconis. In both stars the light 
at minimum is distinctly redder than before. In the 
other paper Mr. R. McDiarmid deals with the 
algol variables, TV, TW, TX Cassiopeiz, and T 
Teonis Minoris. Secondary minima have been estab- 
lished in the light curves of TW Cass. and T Leo. 
NO. 2380, VOL. 95] 


Min. The light curve of TV Cass. indicates an in- 
crease of brightness between primary and secondary 
eclipse, and the light curve of TX Cass. affords 
evidence of darkening towards the limb. 
SHort Prriop VartaBteE Stars.—Von G. Hornig 
(Ast. Nach., No. 4808) publishes the results of 
numerous observations by Argelander’s method of 
several bright variable stars of short period. The 
elements calculated from these observations, together 
with mean light curves, are given for the three 
Cepheid variables RT Aurigze (74 obs.), 7 Aquila 
(190 obs.), 6 Cephei (396 obs.), for the Geminid vari- 
able € Geminorum (171 obs.), and for the two stars 
of 6 Lyre type, » Herculis (208 obs.) and B Lyrz 
(327 obs.). Elements determined by Breson from 
observations of ¢ Geminorum, 7 Aquilz, 8 Cephei, 
and 8 Lyre, and by Lau in the case of 8 Cephei and 
& Lyra, are compared. It is stated that the lack of 
correspondence in the secondary maxima of light 
curves determined by different observers is due to 
their varied ‘‘colour-perception,’? as are also the 
minor differences of more or less pointed or flattened 
maxima. 

THE MANCHESTER MEETING OF THE 
BRITISH ASSOCIATION. 
As 
already announced, the meeting will be opened 
on September 7 and close on September 11. 
The following are among the sectional arrange- 
ments :—In Section A there will be discussions on 
radio-active elements and the periodic law (opened by 
Prof. F. Soddy); spectral classification of stars and 
the order of stellar evolution (opened by Prof. A. 
Fowler); thermionic emission (opened by Prof. O. W. 
Richardson); and papers by Prof. W. H. Bragg and 
W. L. Bragg, on X-rays and crystal structure; G. H. 
Hardy, on prime numbers; and Prof. A. N. White- 
head, on time, space, and relativity. 
In Section B there will be an exhibition and ex- 
planation of diagrams by Dr. Dalton, illustrating his 
atomic theory, an experimental paper by the Hon. 
R. J. Strutt on active nitrogen, a discussion on smoke 
prevention, experimental papers on combustion, a 
paper by Prof. W. J. Pope on liquid crystals (with 
experiments), and a discussion on homogeneous 
catalysis. 
In Section C Dr. G. Hickling will give an account 
of the geology of Manchester and district; Prof. 
W. Boyd Dawkins, papers on the classification of the 
tertiary strata by means of the Eutherian mammals, 
and the geological evidence of the antiquity of man 
in Britain. There will be a joint discussion with 
Section E on the classification of land forms (opened 
by Dr. J. D. Falconer). Papers will be read by Dr. 
A. H. Cox and A. K. Wells on the Ordovician 
sequence in the Cader Idris district (Merioneth); Prof. 
T. G. Bonney, on the north-west region of Charnwood 
Forest; Dr. A. Vaughan, on the shift of the western 
shore-line in England and Wales during the Avonian 
period; Prof. W. G. Fearnsides, on a contour map 
of the Barnsley coal seam in Yorkshire. A discussion 
on radio-active problems in geology (opened by Sir 
E. Rutherford). Papers will be read by Prof. C. A. 
Edwards on twinning in metallic crystals; Prof. W. J. 
Sollas, on the restoration of certain fossils by serial 
sections; Dr. J. W. Evans, on the isolation in the 
directions image of a mineral in a rock-slice; Dr. G. 
Hickling, on the micro-structure of coal; D. M. S. 
Watson, on vertebrate life zones in the Permo-Trias ; 
Dr. A. Wilmore, on the Carboniferous limestone zones 
of north-east Lancashire; H. Day, a brief criticism 
