: 
ADDRESS.. Xxxvll 
more have been found to present that mottled appearance which renders it 
almost a matter of certainty that an increase of optical power would show 
them to be similarly composed. A not unnatural or unfair induction would 
therefore seem to be, that those which resist such resolution do so only in 
consequence of the smallness and closeness of the stars of which they con- 
sist; that, in short, they are only optically and not physically nebulous. 
There is, however, one circumstance which deserves especial remark, and 
which, now that my own observation has extended to the nebule of both he- 
mispheres, I feel able to announce with confidence as a general law, viz. that 
the character of easy resolvability into separate and distinct stars is almost 
entirely confined to nebulz deviating but little from the spherical form ; 
while, on the other hand, very elliptic nebulz, even large and bright ones, 
offer much greater difficulty in this respect. The cause of this difference 
must, of course, be conjectural, but, I believe, it is not possible for any one 
to review seriatim the nebulous contents of the heavens without being satisfied 
of its reality as a physical character. Possibly the limits of the conditions 
of dynamical stability in a spherical cluster may be compatible with less 
numerous and comparatively larger individual constituents than in an elliptic 
one. Be that as it may, though there is no doubt a great number of elliptic 
nebule in which stars have not yet been noticed, yet there are so many in 
which they have, and the gradation is so insensible from the most perfectly 
spherical to the most elongated elliptic form, that the force of the general 
induction is hardly weakened by this peculiarity; and for my own part I 
should have little hesitation in admitting all nebule of this class to be, in fact, 
congeries of stars. And this seems to have been my Father's opinion of their 
constitution, with the exception of certain very peculiar-looking objects, re- 
specting whose nature all opinion must for the present besuspended. Now, 
among all the wonders which the heavens present to our contemplation, there 
is none more astonishing than such close compacted families or communities 
of stars, forming systems either insulated from all others, or in binary con- 
nexion, as double clusters whose confines intermix, and consisting of indivi- 
dual stars nearly equal in apparent magnitude, and crowded together in such 
multitudes as to defy all attempts to count or even to estimate their numbers. 
What are these mysterious families? Under what dynamical conditions do 
they subsist? Is it conceivable that they can exist at all, and endure under 
the Newtonian law of gravitation without perpetual collisions? And, if so, 
what a problem of unimaginable complexity is presented by such a system if 
we should attempt to dive into its perturbations and its conditions of stability 
by the feeble aid of our analysis! The existence of a luminous matter, not 
‘congregated into massive bodies in the nature of stars, but disseminated 
through vast regions of space in a vaporous or cloud-like state, undergoing, 
or awaiting the slow process of aggregation into masses by the power of gra- 
vitation, was originally suggested to the late Sir W. Herschel in his reviews 
of the nebulz, by those extraordinary objects which his researches disclosed, 
which exhibit no regularity of outline, no systematic gradation of brightness, 
but of which the wisps and curls of a cirrhus cloud afford a not inapt deserip- 
tion. The wildest imagination can conceive nothing more capricious than 
their forms, which in many instances seem totally devoid of plan—as much so 
as real clouds,—in others offer traces of a regularity hardly less uncouth and 
characteristic, and which in some cases seems to indicate a cellular, in others 
a sheeted structure, complicated in folds as if agitated by internal winds. 
_ Should the powers of an instrument such as Lord Rosse’s succeed in resol- 
ving these also into stars, and, moreover, in demonstrating the starry nature 
of the regular elliptic nebule, which have hitherto resisted such decomposi- 
tion, the idea of a nebulous matter, in the nature of ashining fluid, or conden- 
1845. d 
