
. 
May 5, 1923] 
NATURE 
615 

of 381 publishers’ remainders. The copies are as 
published, i.e. not second-hand, and the reductions 
_ in many cases are considerable. Several books of 
scientific interest are included. The list should be 
seen by all who are in search of book bargains. 
Tue Oxford University Press announces “ Race 
Problems in the New Africa,” by the Rev. W. C. 
Willoughby, in which will be discussed the relation 
of Bantu and British in the parts of Bantu Africa 
which are under British control. The same house 
will also publish ‘‘ A Practical Hausa Grammar, with 
exercises, vocabularies, and specimen examination 
papers,” by Capt. F. W. Taylor. 
Messrs. A. AND C. Brack, Lrp., have in prepara- 
tion new editions of vol. 2 of Dr. D. H. Scott’s 
“Studies in Fossil Botany ’’ (Spermophyta) and 
vol. r (Radiography) of Dr. R. Knox’s ‘‘ Radiography 
and Radio-therapeutics.’”’ In the first-named work 
the account of the so-called ‘‘ Seed Ferns ”’ (Pterido- 
sperms) has been completed, rearranged, and for the 
most part rewritten. A number of families are 
described more fully than in the previous edition. 
The systematic position of the Pteridosperms is dis- 
cussed, and a new view is taken of this question 
differing widely from that formerly maintained. 
In the second work the opportunity has been taken to 
bring the text up-to-date in regard to the progress of 
radiography, and to include a chapter on the author’s 
recent work on gallstones. The volume also includes 
some appendices, one consisting of a report of the 
committee which was appointed to consider the 
protection of the operator from the effects of over- 
exposure to X-rays or radium. 
Our Astronomical Column. 
THE PRESENT CONDITION OF THE GIANT PLANETS. 
—Some surprise was created at the meeting of the 
Royal Astronomical Society on April 13 by a paper 
from Dr. Harold Jeffreys in which he raised doubts 
about the generally accepted view that these planets 
are still at a very high temperature. He made an 
estimate of the amount of heat that would have been 
radiated by Jupiter in the course of a period of three 
hundred million years, on the assumption of a high 
temperature throughout this period, finding that it 
exceeded the probable initial supply; he drew a 
further argument from the low densities both of 
‘primaries and satellites, in the case of these four 
planets, concluding that they are built of less dense 
materials than the inner planets. While there was 
some agreement with these views at the meeting, 
there were several expressions of dissent. The very 
energetic processes that are obviously going on upon 
Jupiter can scarcely be ascribed to the very feeble 
solar radiation, which is only one-twenty-seventh of 
that received by the earth. Moreover, if Jupiter 
were formed of material of the same density as that 
forming its satellites, the much greater force of 
gravitation upon it would produce a higher density 
through compression, unless counteracted by heat 
or some similar agency. A further argument was 
drawn from the spectra of these planets photographed 
at Flagstaff; these all showed broad absorption 
bands, implying dense atmospheres. 
It will be remembered that recent studies of Jupiter 
by the bolometer indicated no sensible heating effect ; 
but this was ascribed at the time to a dense absorbing 
_ atmosphere rather than to an actually cool interior. 
In any case, it is always in the interests of truth for 
any weighty evidence that can be put forward against 
accepted results to be considered seriously in an 
impartial frame of mind. 
NATURE OF THE SPIRAL NEBUL&.—Recent dis- 
coveries on the rapid rotational motion of the spiral 
nebulae, which has been revealed both by spectro- 
ore determinations of velocity in the line of sight, 
and by Dr. Van Maanen’s discussion of photographs 
_ taken at an interval of some years, has shown that 
these objects are not directly comparable with the 
Galactic system. Their distance can be roughly 
estimated by comparing the angular and linear 
rotational velocities; it is of the order of a few 
thousands of light-years, which is far too small to 
permit us to regard the regions of uniform luminosity 
NO. 2792, VOL. I11] 
as being due to the combined light of millions of 
stars. Prof. Lindemann read a paper before the 
Royal Astronomical Society on April 13 in which he 
put forward the view that they are simply vast 
collections of cosmical dust, the diameters of the 
particles being of the order of 1o~* cm., that being 
the size for which light-pressure is most efficient. 
In other words, as Prof. Turner expressed it in 
the discussion which followed, the spirals are regarded 
as the dustbins of the stellar system, into which all 
interstellar dust is swept by the light-pressure 
exerted by the stars. An explanation would thus be 
afforded of the remarkable freedom from dust of 
the interstellar spaces, which was brought out by 
Prof. Harlow Shapley’s work on the globular clusters, 
and by other researches. Prof. Lindemann suggested 
that the light of the spirals was simply reflected 
light from the whole stellar system ; their spectrum, 
which seems to be a blend of all the stellar types, is 
in accord with this view. The case would be analogous 
to that of the Pleiades nebule, which give the same 
spectra as those of the stars which they surround. 
Prof. Lindemann showed that on certain assumptions 
as to the thickness of the spirals, reflected starlight 
would account for the observed luminosity. The 
mass of the spirals would still be of the order of 
thousands of suns, and they might still be regarded . 
as providing the material of future clusters. 
VARIABLE WITH A REMARKABLE SPECTRUM.— 
Dr. Harlow Shapley, in Harvard College Observatory 
Bulletin No. 783, describes the spectrum and the 
light variation of the tenth magnitude star H.D. 
81137 (R.A. 9% 18-7", Dec. -—52° 8’) as “ both of 
unprecendented types.’ The spectrum belongs to 
the type Ma of the Harvard Classification, and contains 
five well-marked bright lines or bands coinciding with 
some of the strongest bright lines in the spectrum of 
n Carine, the origins of which are unknown. 
The spectrum of » Carine is not classified by the 
Harvard observers but described simply as “‘ peculiar,” 
but it is probably a hot star. H.D. 81137, as it is 
classed Ma, is comparatively a cool star, so this is an 
example of a cool star exhibiting bright lines of a hot 
star nature. Approximate positions of these lines 
are \\ 4244, 4287, 4352 to 4358, 4414 to 4416, and 
4452 to 4457. { : 
The light curve showed a steady rise from 9-8 in 
1890 to 9-2 in roor, and has since steadily dropped, 
reaching 10-1 in May 1922, so the period of variability 
is long. 
