466 
NATURE 
[March 3, 1870 
STAR-DRIFT 
With reference to the accompanying account of my paper on 
this subject, recently communicated to the Royal Society, it is 
to be remarked that the interest, if any, attaching to my results 
must be founded on the way in which they bear on received 
theories respecting the distribution of the fixed stars. It is 
quite evident that according to the views usually accepted, the 
stars which appear in any part of the heavens must be regarded 
as situated at very different distances from the eye ; the faintest 
nine or ten times farther from us, at the very least, than the 
brightest, and the different stars altogether too far apart to 
exert any influence on each other. Indeed, whatever theory we 
may hold respecting stellar distribution, regarded generally, we 
must be prepared to recognise in the stars seen towards any part 
of the sky, objects which lie at very different distances. And 
regarding these objects as severally in motion, we must be pre- 
pared to find in general the utmost diversity, not only as re- 
spects the direction of the apparent motions of the stars, but also as 
respects the magnitude of these motions. It is only when one has 
adopted the theory that the stars are grouped according to 
special laws of aggregation, that one would be led to anticipate 
that here and there, almost as by accident, so to speak, some 
indications of their grouping might be discoverable in the cha- 
racteristics of the stellar proper motions. Although I had 
become firmly convinced that the stars are not distributed 
throughout space with any approach to that general uniformity 
insisted on by many astronomers, I had very little hope that a 
suggestion I threw out a year ago in the pages of the Stdent, 
that the stellar proper motions if examined carefully might 
afford evidence in favour of my views, weuld be confirmed in 
any very distinct manner if the method I had pointed out should 
ever be applied. I knew that a certain community of 
motion in the constellation Taurus had led Madler to im- 
portant, but as I judged incorrect conclusions as to the nature of 
the stellar motions; but I also knew that that community of 
motion was one which could only be appreciated by the few who 
had convinced themselves of what was to be exfected if the stars 
were uniformly distributed. I had an impression at that time 
that Midler had examined the stellar proper motions over the 
whole of the northern hemisphere, and that it was the excep- 
tional community of proper motion in Taurus which had led him 
to form his well-known theory respecting a central sun. It was 
only when I was reminded that he had in fact examined the 
stellar proper motions in the neighbourhood of Taurus alone, 
having been led by independent considerations to regard that 
neighbourhood as that within which a central sun was to be 
looked for, that I was encouraged to map down all the recog- 
nised proper motions. To my surprise I found that in Gemini, 
Cancer, and Leo, a community of motion far more striking than 
that noticed by Madler in Taurus was to be recognised ; and fur- 
ther, that though in other directions, as I had expected, stellar 
motions belonging to different depths in space were intermixed, 
it was yet possible to trace out laws of association indicating the 
existence of drifting star-groups in these directions also. 
I lay very little stress on the indications which have led me to 
name the great double cluster in Perseus as more likely to be an 
important centre of motion than the Pleiades. But it is worthy 
of mention that Madler required a star on the Milky Way as the 
centre of the galaxy, and Alcyone does of lie on the Milky Way; 
he required his centre to lie ninety degrees from the apex of the 
solar motion, and Alcyone does zof lie ninety degrees from the 
mean of the last determinations of that point. ‘The great cluster 
in Perseus fulfils both conditions in the most perfect manner. 
RICHARD A. PROCTOR 
A careful examination of the proper motions of all the fixed 
stars in the catalogues published by Messrs. Main and Stone 
(Memoirs of the Royal Astronomical Society, vols. xxviii. 
and xxxiii.) has led Mr. Proctor to the conclusion that in 
parts of the heavens the stars exhibit a well-marked tendency 
to drift in a definite direction. ‘‘In the catalogues of proper 
motions, owing to the way in which the stars are arranged, 
this tendency is masked; but when the proper motions are indi- 
cated in maps, by affixing to each star a small arrow whose 
length and direction indicate the magnitude and direction of the 
star’s proper motion, the star-drift (as the phenomenon may be 
termed) becomes very evident. It is worthy of notice that 
Madler, having been led by certain considerations to examine 
the neighbourhood of the Pleiades for traces of a community of 
proper motion, founded on the drift he actually found in Taurus 
his well-known theory that Alcyone (the cwcida of the Pleiades) 
is the common centre around which the sidereal system is 
moving. But in reality the community of motion in Taurus 
is only a single instance, and not the most striking that 
might be pointed out, of a characteristic which may be recognized 
in many regions of the heavens. In Gemini and Cancer there 
is a much more striking drift towards the south-east, the drift in 
Taurus being towards the south-west. In the constellation 
Leo there is also a well-marked drift, in this case towards 
Cancer. 
“* These particular instances of star-drift are not the less remark- 
able, that the stars are drifting almost exactly in the direction 
due to the proper motion which has been assigned to the sun, 
because the recent researches of the Astronomer Royal have 
abundantly proved that the apparent proper motions of the stars 
are not to be recognised as principally due to the sun’s 
motion. Mr, Stone has shown even that we must assign to the 
stars a larger proper motion, on the average, than that which 
the sun possesses. Looking, therefore, on the stars as sever- 
ally in motion, with velocities exceeding the sun’s on the 
average, it cannot but be looked upon as highly significant 
that in any large region of the heavens there should be a 
community of. motion such as I have described. We seem 
compelled to look upon the stars which exhibit such community 
of motion as forming a distinct system, the members of which 
are associated indeed with the galactic system, but are much 
more intimately related to each others In other parts of the 
heavens, however, there are instances of a star-drift opposed to 
the direction due to the solar motion, A remarkable instance 
may be recognised among the seven bright stars of Ursa Major. Of 
these, the stars B, y, 5, «, and Care all drifting in the same direction, 
and almost exactly at the same rate towards the “apex of the solar 
motion,” that is, the point /vo which all the motions due to the 
sun’s translation in space should be directed. If these five stars, 
indeed, form a system (and I can see no other reasonable expla- 
nation of so singular a community of motion), the mind is lost 
in contemplating the immensity of the periods which the revyo- 
lutions of the components of the system must occupy. Madler 
had already assigned to the revolution of Alcor around Mizar 
(¢ Ursee) a period of more than 7000 years. But if these stars, 
which appear so close to the naked eye, have a period of such 
length, what must be the cyclic periods of stars which cover a 
range of several degrees upon the heavens? In like manner the 
stars a, B, and y Arietis appear to form a single system, 
though the motion of a is not absolutely coincident either in mag- 
nitude or direction with that of B andy, which are moving on 
absolutely parallel lines with equal velocity. There are many 
other interesting cases of the same kind.” The author hopes 
soon to be able to lay before the Royal Society a pair of maps in 
which all the well-recognised proper motions in both hemi- 
spheres are exhibited on the stereographic projection. In the 
same maps also the effects due to the solar motion are exhibited 
by means of great circles through the apex of the solar motion, 
and small circles or parallels having that apex for a pole. The 
star-drift described by Mr. Proctor serves to explain several phe- 
nomena which had hitherto been thought very perplexing. In the 
first place, it accounts for the small effect which the correction due 
to the solar motion has been found to have in diminishing the sums 
of the squares of the stellar proper motions. Again, it explains 
the fact that many double stars which have a common proper 
motion, appear to have no motion of revolution around each 
other; for clearly two members of a drifting system might 
appear to form a close double, and yet be in reality far apart 
and travelling, not around each other, but around the centre 
of gravity of the much larger system they form part of. While 
mapping the proper motions of the stars, Mr. Proctor has been 
led to notice that the rich cluster around x Persei falls almost 
exactly on the intersection of the Milky Way with the great 
circle which may be termed the equator of the solar motion ; 
that is, the great circle having the apex of the sun’s motion as a 
pole. This circumstance points to that remarkable cluster, 
rather than to the Pleiades, as the centre of the sidereal system, 
if indeed that system has a centre cognisable by us. When we 
remember that for every fixed star in the Pleiades there are 
hundreds in the great cluster in Perseus, the latter will seem the 
worthier region to be he centre of motion, The author is dis- 
posed, however, to regard the cluster in Perseus as the centre of 
a portion of the sidereal system, rather than as the common centre 
of the Galaxy. 
