THE PHYSICAL PHENOMENA OP OTHEE WOELDS. 313 
learns tliat tliere are twin worlds^ one of these being often a 
self-lnniinons sun, and the other a dark sphere of correspond- 
ing size. But, having observed all these, he finds the space- 
penetrating instrument fails him ; and remote in regions 
beyond the power of human measurement, he still is conscious 
of a luminous scattering, which can only be described as 
star-dust."’^ 
Isolated systems of stars have been alluded to ; on these a 
few words more. Sir J ohn Herschel says, In the constella- 
tion Cancer there is a somewhat similar but less definite 
luminous spot, called Prsesepe, or the bee-hive, which a very 
moderate telescope — an ordinary night-glass, for instance — 
resolves entirely into stars. In the sword-handle of Perseus, 
also, is another such spot crowded with stars, which requires 
rather a better telescope to resolve into individuals separated 
from each other.'’"’ These clusters of stars ■’^ were regarded 
by Sir William Herschel as masses of matter revolving round 
a common centre, and gradually approaching by their mutual 
attraction; but their order, their variety, and their beauty 
rather tell against this hypothesis. Among the most 
beautiful objects of this class — again we quote Sm John 
Herschel — ^‘"is that which surrounds the star k Crucis, set 
down as a nebula by Lacaille. It occupies an area of about 
one forty-eighth part of a square degree, and consists of about 
110 stars, from the 7th magnitude downwards, eight of the 
more conspicuous of which are coloured with various shades of 
red, green, and blue, so as to give to the whole the appearance 
of a rich piece of jewellery.-’-’ Is it not more probable that we 
see in such systems as those the conditions of our own solar 
system varied and enlarged, the power of gravitation dravdng 
the smaller wanderers towards their central sun, while the 
rates of their motions are so determined — so balanced against 
gravitation — ^that they move onward ^^in their courses -’-’ without 
deviation for ever ? 
The Milky Way is, probably, but a mighty extension of this 
or some such condition. Even our own Sun and his attendant 
worlds may be plunged in a vast stratum of stars; amidst 
which it performs in independence its internal laws ^-’ while 
moving with the whole — a vast sidereal ring — around some 
common centre. However, independently of the clusters of 
stars we have unresolvable nebulae, which were well described 
by Halley as being like the matter of a comet^s tail — a 
phosphorescent vapour or a gaseous and elementary form of 
luminous sidereal matter. We have endeavoured — though 
hastily and, consequently, imperfectly — to carry the mind of 
the reader from the system of Sun and planets to which we 
belong — through the multitudes of stars varying in their 
