Clusters and Nebulae. — Occultation. 387 



sun, or Sirius, or Wega. Setting aside for the present the 

 inevitable inference from spectrum-analysis^ it certainly seems 

 very difficult to ascribe a starry nature to such luminous 

 masses as the Andromeda nebula, or its analogue M. 81. It is 

 easy to find cases of resolution, separately, of either a very 

 feeble mist, or a very brilliant and blazing nucleus. But it is 

 not easy to conceive the combination of these two in one 

 object, as in those instances. The stars whose light compose 

 that faint haze, so diffuse that it has no assignable termination, but 

 dies imperceptibly into the dark sky, and can perhaps only be 

 traced in its full extent by a rapid movement of the telescope, 

 must be individually so excessively minute, that such an accu- 

 mulation of them as would form a bright and vivid nucleus is 

 quite beyond the bounds of probability. No justifiable stretch 

 of imagination could compound the central blaze of those 

 nebulae out of materials individually less perceptible than the 

 20th mag. of H., or the 13th of O.2. We might indeed have 

 recourse to the supposition that the components all progres- 

 sively increase in magnitude or luminosity towards the centre ; 

 but this, not to mention that it finds little countenance in the 

 known arrangement of stars of various sizes in globular 

 clusters, of which two instances have been given in the present 

 article, is liable to the grave objection of being a special and 

 gratuitous assumption in order to escape from a difficulty. On 

 the other hand, the bare inspection of these nebulas conveys 

 the strong impression of an uniform material, capable either of 

 great extremes of condensation and rarefaction, or of very vary- 

 ing degrees of luminosity dependent upon unequal temperature, 

 and therefore, in all probability, neither solid nor fluid, unless 

 it might be in a state of extreme division. In short, we can 

 conceive these objects to be an incandescence of either gas, 

 or mist — that is, exceedingly comminuted fluid ; or dust — that 

 is, similarly attenuated solid matter; but we can scarcely 

 reconcile their aspect with a stellar composition. Had the 

 spectroscope told us unequivocally that we were wrong, we 

 must have given way to its decision; but we see that its 

 verdict is so far ambiguous as not altogether to shut up the 

 inquiry. 



OCCULTATION. 

 June loth, B.A.C. 5579, 5 mag. 7h. 7m. to 7h. 41m. 



