DECEMBER 21, 1916] 
OUR ASTRONOMICAL COLUMN. 
ROmer’s DiscovERY OF THE VELOCITY oF LIGHT 
(‘Om Ole Romers ‘Opdagelse of* Lysets Toven": 
Host & Son, Kobenhavn).—When Romer in 1676 
announced to the Paris Academy his discovery of the 
SB Seg propagation of light from observations of the 
rst satellite of Jupiter in the course of eight years, 
he gave no details as to these observations. He merely 
stated that the period of revolution of the satellite 
deduced from immersions in the shadow of Jupiter 
(when the earth is approaching Jupiter) was always 
shorter than the period found from emersions observed 
when the earth was receding from the planet. The 
result was that light took about twenty-two minutes 
to travel over the diameter of the earth’s orbit. (It 
appears from a letter to Huygens that this was found 
from observations made in 1671~73.) The only ob- 
servation quoted in the short paper was one of an 
emersion on November 9, 1676, at 5h. 35m. 45S. p.m., 
ten minutes later than was calculated from observa- 
tions in the previous August, as predicted by Rémer 
in the beginning of September. Three years ago a 
sheet was found in the University Library at Copen- 
hagen on which was written in Rémer’s hand a list 
of eclipses of the satellites observed in the years 
1668-77. In a paper published in the Transactions 
of the Danish Academy of Sciences Mrs. Kirstine 
Meyer discusses these observations in order to find 
whether they represent a part of the material on which 
Roémer’s discovery was based, and shows that this is 
really the case. It is shown by several examples that 
the observations of 1671-73 give, in fact, the approxi- 
mate result announced by Romer, but that the single 
results differ a good deal. It is interesting to see 
from some figures jotted down by Rémer in the MS. 
in question that among the values found by him for 
the time light takes to pass from the sun to the earth 
is also the correct one of about eight minutes, but he 
probably rejected this result as founded on rather short 
intervals of time. The author calculates the amount 
resulting from the published observation of November, 
1676, and finds that it is eight and a half minutes. 
Curiously enough, Newton, in his ‘Optics,’ gives 
eight minutes, though the only result published by 
Romer was about eleven minutes. 
PARALLAXES OF Two STARS WITH Common Mortion.— 
Some time ago it was found by Adams that the two 
stars, A.Oe. 14318 and 14320, though separated by 5/ 
in declination, had remarkably similar proper motions 
and radial velocities. The parallaxes and proper 
motions in R.A. of these interesting objects have since 
been determined by O. J. Lee from plates taken with 
the 4o-in. refractor of the Yerkes Observatory (Astro- 
nomical Journal, No. 697). The resulting parallaxes 
are 0:025"+0-008" and 0-061"+0-012", and the proper 
motions in R.A. —o-o699s. and —o-o692s. respectively. 
More trustworthy determinations of proper motion by 
Prof. J. G. Porter give the total motions as 3-693” in 
the direction 195-7°. and 3-675" in the direction 195-6°. 
The difference of parallax, amounting to 0-036", agrees 
well with the value 0-031" previously given by Russell, 
and the evidence that the two stars are very Widely 
separated in space, while having practically identical 
motions both in and across the line of sight, is now 
fairly conclusive. It may be recalled that the two 
stars are of magnitudes 9-6 and 9-2, and of types G4 
and G5 respectively. The radial velocities are 
exceptionally great, being +307 km./sec. and 
+295 km./sec., according to the observations 
of Adams, and the difference. is probably — not 
greater than the errors of observation in the case 
of such faint stars. The two stars have the same 
R.A., 15h. 5-5m., while the declinations are —16° 2-5/ 
and —15° 57-5), 
NO. 2460, VOL. 98] 
NATURE 
17 
2 
J 
THE DIRECT JOINING OF GLASS .AT 
MODERATE TEMPERATURES. 
[N a paper presented to the Faraday Society on 
December 18, Messrs. Parker and Dalladay de- 
scribed some interesting experiments on the direct join- 
ing of glass at relatively low temperatures which they 
have carried out in the research laboratories of Messrs. 
Adam Hilger, Ltd. The results described are not 
only of very considerable direct scientific interest, but 
afford great practical advantages in the construction 
of glass apparatus out of what is actually a single 
solid piece instead of using more or less unsatisfactory 
cements. The advantage of such solid construction is 
particularly evident in polarimeter tubes and absorption 
cells—the latter can now be constructed with truly 
parallel faces and with inside faces optically worked. 
The process of joining which the authors have worked 
out consists in placing the surfaces of glass to be 
united in good optical contact under pressure, and 
then raising the temperature to a carefully determined 
degree. The glass surfaces thus treated become per- 
fectly united, so that the two pieces of glass will not 
separate along their former interface, and the com- 
posite piece acts as if it were a single solid mass; even 
a orack or a diamond-cut will pass through the junc- _ 
tion without hindrance or deflection. The temperature 
employed is chosen as high as possible in order to 
lessen the time required for union of the surfaces, 
but if distortion of the optically worked surfaces is 
to be avoided, then the temperature must not be taken 
too near the limit, which the authors describe as the 
“annealing point.’ This point they determine by 
observing the strains set up in a piece of glass while being 
heated at a definite rate in an electric-tube furnace; 
for each kind of glass they find that these internal 
stresses—which are readily observed by means of 
polarised light—disappear quite suddenly. At this 
point, also, the glass becomes appreciably soft, and can 
be indented by a sharp tool. When similar kinds of 
glass are used, having similar ‘annealing points,” 
then the welding of surfaces in optical contact tales 
place well below this annealing point. Very dissimilar 
glasses, however, cannot well be joined, since the 
softer becomes distorted before the harder is hot 
enough to weld freely. 
THE EXPLOITATION OF INSHORE 
FISHERIES. 
WAN* advisory and other committees, some in con- 
nection with the great Government departments 
and others among the leading scientific societies, are 
at present engaged in deliberations in regard not 
only to immediate and pressing war problems, but 
also to the later, and possibly equally important, 
after-war questions, which are bound to arise, affecting 
the prosperity of the country and the maintenance of 
the Empire. A large number of these matters turn 
upon the application of scientific knowledge and scien- 
tific methods to various industries, and amongst these 
not the least important are those concerned with the 
allied subjects of agriculture and aquiculture, or the 
scientific regulation and cultivation of our land crops 
and our sea-fisheries. 
It is recognised that, with the view of making a 
rapid recovery from the effects of the war, amongst 
other things, agriculture and allied industries must 
be promoted, and it must be seen to that no suitable 
land is wasted, that none is applied to the wrong pur- 
pose, and that the most favourable treatment to ensure 
the best results is given to each area. In fact, a more 
1 Introductory address (abridged) given by Prof. W. A. Herdman, F.R.S., 
in opening the discussion om Inshore Fisheries in the section of Zoology of 
the British Association at Newcastle-upon-Tyne on September 7. 
