VOL. LXXV.J PHILOSOPHICAL TRANSACTIONS. 687 



and here I must observe, that the difference between a crowded place and a cluster 

 may easily be perceived by the arrangement as well as the size and mutual dis- 

 tance of the stars: for in a cluster they are generally not only resembling each 

 other pretty nearly in size, but a certain uniformity of distance also takes place; 

 they are more and more accumulated towards the centre, and put on all the ap- 

 pearances which we should naturally expect from a number of them collected 

 into a group at a certain distance from us. On the other hand, the rich parts of 

 the milky way, as well as those in the distant broad part of the stratum, consist 

 of a mixture of stars of all possible sizes, that are seemingly placed without any 

 particular apparent order. Perhaps we might recollect, that a greater condensa- 

 tion towards the centre of our system, than towards the borders of it, should be 

 taken into consideration ; but, with a nebula of the 3d form, containing such 

 various and extensive combinations, as I have found to take place in ours, this 

 circumstance, which, in one of the first form, would be of considerable mo- 

 ment, may I think be safely neglected. However, I would not be understood to 

 lay a greater stress on these and the following calculations than the principles on 

 which they are founded will permit ; and if hereafter we shall find reason, from 

 experience and observation, to believe that there are parts of our system where 

 the stars are not scattered in the manner here supposed, we might then make 

 proper exceptions. 



Mr. H. then tries the effect of another high gage, which, by a process of 

 calculation and reasoning like the preceding, gives a similar conclusion in the 

 number of the stars, &c. He then continues to remark, that these would not 

 be so close but that a good power applied to a proper instrument might easily dis- 

 tinguish them ; for they need not, if arranged in regular squares, approach 

 nearer to each other than 6". '27 ; but what would produce the milky nebulosity 

 which I have mentioned, is the numberless stars beyond them, which in one 

 respect the visual ray might also be said to reach. To make this appear we must 

 return to the naked eye, which, as before estimated, can only see the stars of 

 the 7th magnitude so as to distinguish them ; yet it is very evident that the 

 united lustre of millions of stars, such as I suppose the nebula in Andromeda 

 to be, will reach our sight in the shape of a very small, faint nebulosity ; since 

 the nebula of which I speak may easily be seen in a fine evening. In the same 

 manner my present telescope has not only a visual ray that will reach the stars at 

 497 times the distance of Sirius so as to distinguish them, and probably much 

 farther, but also a power of showing the united lustre of the accumulated stars 

 that compose a milky nebulosity, at a distance far exceeding the former limits : 

 so that from these considerations it appears highly probable that my present teles- 

 cope, not showing such a nebulosity in the milky way, goes already far beyond 

 its extent : and consequently, much more would a more powerful instrument 



