592 PHILOSOPHICAL TRANSACTIONS. [aNNO IJSg, 



some additional circumstances in the appearance of extended clusters and nebulae, 

 that very much favour the idea of a power lodged in the brightest part. Though 

 the form of them be not globular, it is plainly to be seen that there is a ten- 

 dency towards sphericity, by the swell of the dimensions the nearer we draw to- 

 wards the most luminous place, denoting as it were a course, or tide of stars, 

 setting towards a centre. x\nd — if allegorical expressions may be allowed — it 

 should seem as if the stars thus flocking towards the seat of power were stemmed 

 by the crowd of those already assembled, and that while some of them are suc- 

 cessful in forcing their predecessors sideways out of their places, others are them- 

 selves obliged to take up with lateral situations, while all of them seem equally 

 to strive for a place in the central swelling, and generating spherical figure. 

 Since then almost all the nebulae and clusters of stars I have seen, the number 

 of which is not less than three and twenty hundred, are more condensed and 

 brighter in the middle ; and since, from every form, it is now equally apparent 

 that the central accumulation or brightness must be the result of central powers, 

 we may venture to affirm that this theory is no longer an unfounded hypothesis, 

 but is fully established on grounds which cannot be overturned. 



Let us endeavour to make some use of this important view of the constructing 

 cause, which can thus model sidereal systems. Perhaps, by placing before us 

 the very extensive and varied collection of clusters and nebulae, furnished by my 

 catalogues, we may be able to trace the progress of its operation, in the great 

 laboratory of the universe. If these clusters and nebulae were all of the same 

 shape, and had the same gradual condensation, we should make but little pro- 

 gress in this inquiry ; but, as we find so great a variety in their appearances, we 

 shall be much sooner at a loss how to account for such various phenomena, than 

 be in want of materials on which to exercise our inquisitive endeavours. 



Some ©f these round clusters consist of stars of a certain magnitude, and 

 given degree of compression, while the whole cluster itself takes up a space of 

 perhaps 10 minutes ; others appear to be made up of stars that are much 

 smaller, and much more compressed, when at the same time the cluster itself 

 subtends a much smaller angle, such as 5 minutes. This diminution of the 

 apparent size, and compression of stars, as well as diameter of the cluster to 4, 

 3, 1 minutes, may very consistently be ascribed to the different distances of 

 these clusters from the place in which we observe them ; in all which cases we 

 may admit a general equality of the sizes, and compression of the stars that 

 compose them, to take place. It is also highly probable that a continuation of 

 such decreasing magnitudes, and increasing compression, will justly account for 

 the appearance of round, easily resolvable, nebulae ; where there is almost a 

 certainty of their being clusters of stars. And no astronomer can hesitate to go 



