540 
NATURE 
OUR ASTRONOMICAL COLUMN. 
TurtLe’s Nesuta, N.G.C. 6643.—In this column 
for September 25 last attention was directed to M. 
Borrelly’s observation of Hind’s nebula indicating its 
variable nature. M. Borrelly has recently been making 
observations on the nebula of Tuttle, N.G.C. 6643, at 
the Marseilles Observatory, and has communicated 
the results to the Comptes rendus for December 22, 
1913 (vol. clvii., No. 25, p. 1377). He brings together 
all the observations made since its discovery in 1859, 
and the evidence is distinctly in favour of its vari- 
ability. In very recent years, i.e. in 1909, its light 
appeared to diminish considerably. From i1g10 to 
1912 it was feeble, but still to be seen in the comet- 
seeker (mag. 11). On July 10, 1913, M. Borrelly says 
it was scarcely visible in the instrument; on August 
26 it was at the limit of visibility, while on August 27 
it was practically invisible (mag. 11-5). From the 
observations M. Borrelly concludes that changes have 
taken place. 
Bright HyproGen LIiNEs IN STELLAR SPECTRA AND 
P Cyeni.—Mr. Paul W. Merril communicates two 
papers to the Lick Observatory Bulletin, No. 246. 
The first is the description of a series of spectrograms 
of stars the spectra of which contain bright hydrogen 
lines, and is a continuation of the work described in 
the previous bulletin, No. 162 (1913). The spectra are 
confined to the Ha region, and were obtained with 
the 36-in. refractor and a one-prism spectrograph pre- 
viously described. The stars here dealt with belong 
to classes B and A, but stars of class Oes5 were photo- 
graphed to test their relation to class B. In the last- 
mentioned case, although only a few stars were photo- 
graphed, the evidence was negative, out of nine stars 
none of them indicated bright hydrogen lines. The 
second paper is on the spectrum of P Cygni between 
44340 and A4650, taken with the three-prism spectro- 
graph. Twelve photographs are discussed, having 
been taken between August, 1907, and September, 
1913. Tables are given showing the determined dis- 
placements for numerous lines of H, He, O, N, and 
Si, from each of the photographs. Attention is directed 
to the resemblance between the hydrogen lines of 
P Cygni, and those of an ordinary Nova. It is stated 
that the measurements given in the tables show good 
agreement with those of Frost. 
MEASUREMENT OF SMALL DISPLACEMENTS OF SPEC- 
TRUM Lings.—Bulletin No. 32 of the Kodaikanal Ob- 
servatory contains an important communication by 
Mr. J. Evershed on a new method of measuring small 
displacements of spectrum lines. The main idea of 
the method consists in placing a positive copy of the 
plate to be measured reversed, and almost in contact 
with the negative, film to film, and moving one with 
reference to the other, so that the positive images 
are made to coincide successively with the negative 
images of the corresponding lines. No spider thread is 
used, and the accuracy of the adjustment for coin- 
cidence depends on the sensitiveness of the eye in esti- 
mating the change from the bright and dark con- 
tiguous images of a line, to the perfectly uniform 
density which results when the positive image exactly 
coincides with the negative, and the positive copy has 
the same gradation of tone as the negative. Mr. 
Evershed describes and illustrates the method and 
machine employed, and points out its advantages and 
disadvantages. He also gives two examples of 
measures made in the ordinary way and by the new 
method to show the relative accuracy obtained; these 
represent two series of solar rotation plates. The 
results indicate that the probable error is about halved 
in the positive on negative measures as compared with 
the ordinary measures, and the gain in accuracy is 
NO. 2306, VOL. 92] 
[JANuaRy 8, 1914 
about the same whatever way the probable errors aré 
estimated. 
ASTRONOMICAL ANNUALS AND STAR Cuarts.—The 
annual ‘‘Companion to The Observatory’ has nearly 
become standardised in form, and the present issue 
will be found as useful as ever. The favourable and 
accessible total eclipse of the sun on August 20-21 
next calls for extra information, and this has been 
given in the form of the sun’s altitude, azimuth, and 
parallactic angle for the more accessible part of the 
line of totality in addition to the usual data. For the 
fiftieth year the handy astronomical and meteoro- 
logical annual, edited by M. Camille Flammarion, 
makes its appearance, and the great amount of in- | 
teresting matter contained within its covers is as com- 
plete and useful as in previous issues. Space does 
not allow one to enter into any detail regarding the 
wide range of the information here brought together, 
but astronomical readers are sufficiently acquainted 
with previous volumes to know the utility of the in- 
formation displayed. As is usual, a number of excel- 
lent illustrations and figures accompany the text. Mrs. 
H. Periam Hawkins’s “Star Almanac for 1914”’ and 
“Revolving Star Map” will be found very useful to 
astronomers generally. The former consists of a large 
sheet to be hung up on a wall, and contains much 
useful matter relative to the apparent stellar move- 
ments, meteor showers, planets, &c. The latter is a 
well-constructed planisphere for stars seen from the 
northern hemisphere, and has a movable declination 
scale. 
PRIZE SUBJECTS PROPOSED BY THE 
PARIS ACADEMY OF SCIENCES FOR 1915. 
Geometry.—Francceur prize (1000 frances), for dis- 
coveries or works useful to the progress of pure or 
applied mathematics; Bordin prize (3000 francs), to 
make notable progress in the study of curves with 
constant torsion; to determine, if possible, which of 
these curves are algebraic, at least those which are 
unicursal. 
Mechanics.—A Montyon prize (7oo francs), for the 
invention or improvement of instruments useful to the 
progress of agriculture, the mechanical arts or 
science; Poncelet prize (2000 francs), for work on 
applied mathematics; Boileau prize (1300 francs), for 
researches on the motion of fluids contributing to the 
progress of hydraulics. 
Navigation.—The extraordinary prize of 6000 francs 
for work leading to increased efficiency of the French 
naval forces; Plumey prize (4000 francs), for improve- 
ments in steam engines or any other invention con- 
tributing to the progress of steam navigation. 
Astronomy.—Pierre Guzman prize (100,000 francs), 
to anyone finding a means of communication with 
another planet other than Mars. Failing the above, 
the accumulated interest of five years will be awarded . 
for* an important astronomical discovery. Lalande 
prize (540 francs), for memoir or work useful to the 
progress of astronomy; Valz prize (460 frances), to the - 
author of the most interesting astronomical observa- 
tion during the year; G. de Pontécoulant prize (700 
frances), for researches in celestial mechanics. 
Geography.—Tchihatchef prize (3000 francs), as 
recompense or encouragement to naturalists of any 
nationality distinguished in. the exploration of the 
lesser-known parts of Asia; Gay prize (1500 francs), 
for a study of the distribution of plants in Indo-China. 
Physics.—Heébert prize (1000 francs), for a treatise 
or discovery in connection with the practical use of 
electricity; Hughes prize (2500 francs), for discoveries 
or works contributing to the progress of physics; 
Henri de Parville prize (1500 frances), for original work 
