AucusT 8, 1912] 
NATURE £89 
OUR ASTRONOMICAL COLUMN. 
THe SpecrrumM or Nova Geminorum No. 2.— 
No. 4592 of the Astronomische Nachrichten contains 
two papers dealing with the apparent absorption lines 
in the spectrum of Nova Geminorum No. 2. 
In the first, Herr R. Furuhjelm discusses spectra 
taken with the one-prism spectrograph attached to 
the So-cm. refractor at Potsdam Observatory, and 
finds coincidences between the fine dark lines in the 
nova spectrum, between A3850 and A46s50, and the 
spark lines of Ti, Sc, and Sr, and possibly of Fe and 
Yt, having intensities of 15 or more in the lists of 
Exner and Haschek. He does this by first deriving 
a mean apparent radial velocity of —541 kms. from 
the shifts of all the lines, and applying this as a correc- 
tion to the laboratory wave-lengths; the latter differ 
from the measured nova wave-lengths by about 7 A 
In the spectrum taken on March 15 he is able to fit 
all the Ti, Sc, and Sr lines, numbering 10, 7, and 2 
respectively, and 4 each of the 5 Fe and 5 Yt lines; 
20 is the limiting intensity in the latter case. The 
differences between his calculated and observed wave- 
lengths range from —121 to +136 A. 
Herr Furuhjelm also compares his lines with the 
lines for these same elements, of intensity 5 and over, 
in Dyson’s list of chromospheric lines, and finds that 
there are only six lines in the chromospheric spectrum 
not found in that of the nova, and these lines belong 
to other elements. 
Negatives taken on later dates did not afford so 
many, or so close, coincidences, and the necessary 
compensation for displacement varied considerably. 
Herr Furuhjelm concludes that the apparent radial- 
velocities vary too much to be considered as real, two 
negatives taken on March 17 giving very different 
values. 
Dr. Ludendorff, on a negative secured with spectro- 
graph iv., at Potsdam, on March 15, finds that 37 of 
the dark nova lines between A4310 and 4530 coincide 
with lines in Rowland’s table, with differences corre- 
sponding to radial velocities ranging from +19 to 
+82 kms.; the mean is +49 kms., giving a helio- 
centric radial velocity of +20 kms. He also com- 
pares his lines with the radium, uranium, and emana- 
tion lines falling in this region. The agreement for 
radium and the emanation is very uncertain, and for 
uranium negative, while the radial velocities are very 
different from those found by Dr. Giebeler. From his 
results, Dr. Ludendorff does not venture to answer 
the question as to the presence of these radio-active 
elements in the nova. 
OBSERVATIONS OF JUPITER.—The transit of the 
minor planet Lutetia across Jupiter on May 7 took 
place too early to be observed at the Yerkes Observa- 
tory, but Prof. Barnard made observations of the 
great red spot and of a transit of satellite ii. on that 
date, and records them in No. 4591 of the Astro- 
nomische Nachrichten. The spot was fairly well seen, 
and the bay north of it was, as usual, well defined. 
The southern edge of the spot was in contact with, 
or partly overlapped by, a heavy, irregular, and some- 
what narrow, dark belt. At r8h. om. there was a 
long, dusky marking on the following limb of the 
planet, in the same latitude as the spot, which subse- 
quently would overtake the spot and probably provide 
some interesting phenomena. 
Herr Archenhold observed the spot at Treptow, and 
recorded its transit at rth. 375m. (M.E.T.) on July 
12; this gives a correction of +4m. to Herr Kritz- 
inger’s ephemeris. The spot appeared intensely 
white, without any trace of colour, while the 
‘ streifen appeared to have a rosy-brown hue. 
NO. 2232, VOL. 89| 
THe THREE-PRISM SPECTROGRAPH aT Mount WiILson. 
—A most interesting description of the three-prism 
spectrograph constructed for use with the 60-in. re- 
flector, in its Cassegrain form, at Mount Wilson, is 
published by Prof. Adams in No. 3, vol. xxxv., of 
The Astrophysical Journal. He also describes the 
method of working the instrument and reducing the 
plates, and gives a list of fifty stars, mainly of types 
A and B, that have been found to have variable radial 
velocities. The programme of work is directed to the 
measurement of the radial velocities of stars for which 
Boss has already determined proper motions, and the 
results are expected to provide valuable data for the 
study of star streams. Several stars have been found 
to have one or more hydrogen lines bright, and a 
table is also given of seven stars having very large 
radial velocities. Most of these are of the later types, 
and show radial velocities ranging from 96 to 170 
kms.; their actual velocities in space were calculated 
and range from 119 to 343 kms. per sec. One star, 
Lalande 28607, is notable because it is of the A type, 
and has a radial velocity of —170 kms.; no other 
star of this type is known to have a constant velocity 
approaching this in magnitude. 
THE INSTITUTION OF MECHANICAL 
ENGINEERS. 
HE summer meeting of the Institution of 
Mechanical Engineers opened on Tuesday, July 
30, in Belfast, and terminated on Friday, August 2. 
Papers were read and discussed on ‘Tuesday and 
Wednesday mornings in the Municipal Technical In- 
stitute. As is customary during this meeting, a 
special feature was made of visits to works and points 
of interest to engineers in the neighbourhood of Bel- 
fast. 
A paper dealing with rolling-stock on the principal 
Irish railways was read by Mr. R. M. Livesey, loco- 
motive superintendent, Co. Donegal Railways Joint 
Committee. Practically the only reason for the con- 
struction of a narrow-gauge line is cheapness, and no 
doubt in certain cases a considerable saving can be 
effected. But if, as in many instances in Ireland, 
such railway has to be fully equipped, almost on the 
same lines as a broad-gauge railway, in order to 
comply with the somewhat onerous requirements of 
the Board of Trade, then there is very little to be 
gained from the point of view of economy. The 
author quoted one such railway which cost 11,500l. 
per mile, although no really heavy work was involved 
in its construction. No railway should be built of 
narrow-gauge if the cost will exceed s5o00ol. per mile, 
and then only if the proposed line will be for ever 
isolated from those of standard gauge, and the traffic 
is always likely to be small. The mileage of narrow- 
gauge lines in Ireland is 525, nearly all of which is 
3-ft. gauge. It seems regrettable that the majority 
were not linked up to ferm one large system. The 
author gives particulars and illustrations of typical 
locomotives and cars used on these lines. 
Mr. W. Redfern Kelly, engineer-in-chief to the 
Belfast Harbour Commissioners, presented a paper on 
the new graving dock at Belfast. This dock is the 
only graving dock in which it is possible to place the 
Olympic, the world’s largest specimen of naval archi- 
tecture. The Belfast Harbour Commissioners have 
expended on this dock and its collateral works no less 
than 350,o00l1. ‘The works were commenced in 1904, 
and were finished in about seven years. The length 
over all is gor ft., the breadth is 128 ft. from coping 
to coping, and 96 ft. at the entrance. Full descrip- 
tions and illustrations were given by the author of 
