LO THE SUN’S MOTION IN SPACE. 
ties. They tell nothing as to the value of the perspective element they 
may be supposed to include, or as the real rate of going of the bodies they 
are attributed to, until the size of the sphere upon which they are meas- 
ured has been otherwise ascertained. But the displacements of lines 
in stellar spectra give directly the actual velocities relative to the earth 
of the observed stars. The question of their distances is therefore at 
once eliminated. Now, the radial component of stellar motion is mixed 
up precisely in the same way as the tangential component with the 
solar movement; and since complete knowledge of it in a sufficient 
number of cases is rapidly becoming accessible, while knowledge of 
tangential velocity must for a long time remain partial or uncertain, the 
advantage of replacing the discussion of proper motions by that of 
motions in line of sight is obvious and immediate. And the admirable 
work carried on at Potsdam during the last three years will soon afford 
the means of doing so in the first, if only a preliminary, investigation 
of the solar translation based upon measurements of photographed 
stellar spectra. 
The difficulties, then, caused either by inaccuracies in star catalogues 
or by ignorance of star distances, may be overcome; but there is a 
third, impossible at present to be surmounted, and not without misgiv- 
ing to be passed by. All inquiries upon the subject of the advance of 
our system through space start with a hypothesis most unlikely to be 
true. The method uniformly adopted in them—and no other is avail- 
able—is to treat the inherent motions of the stars (their so-called motus 
peculiares) as pursued indifferently in all directions. The steady drift 
extricable from them by rules founded upon the seience of probabili- 
ties is presumed to be solar motion visually transferred to them in pro- 
portions varying with their remoteness in space and their situations on 
the sphere. If this presumption be in any degree baseless, the result 
of the inquiry is pro tanto falsified. Unless the deviations from the 
parallactic line of the stellar motions balance one another on the whole, 
their discussion may easily be as fruitless as that of observations 
tainted with systematic errors. It is scarcely however doubtful that 
law, and not chance, governs the sidereal revolutions. The point open 
to question is whether the workings of law may not be so exceedingly 
intricate as to produce a grand sum total of results which, from the geo- 
metrical side, may justifiably be regarded as casual. 
The search for evidence of a general plan in the wanderings of the 
stars over the face of the sky has so far proved fruitless. Local con- 
cert can be traced, but no widely-diffused preference for one direction 
over any other makes itself definitely felt. Some regard, nevertheless, 
must be paid by them to the plane of the Milky Way; since it is alto- 
gether incredible that the actual construction of the heavens is with- 
out dependence upon the method of their revolutions. 
The apparent anomaly vanishes upon the consideration of the pro- 
fundities of space and time in which the fundamental design of the 
Sidereal universe lies buried, Its composition out of an indefinite 
