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rius, &c. These indeed, as well as all other heavenly bodies, cannot 

 be said to be entirely free from the influence of the stars surrounding 

 them ; but the character assigned to them is, that the attraction in 

 one direction is so counteracted by a contrary influence of the same 

 nature, as to be retained for many ages in a state almost equal to 

 undisturbed rest. Dr. Herschel suspects that we are to look for solar 

 systems only among those insulated stars. 



2. Binary sidereal systems, or double stars. It is sufficiently ob- 

 vious that these are not stars seen nearly in the same visual ray, for 

 these rays may be an immense distance from each other ; but by 

 these are meant two stars that are connected together by the in- 

 fluence of attraction. It is easy to prove, by the doctrine of gravi- 

 tation, that two stars thus connected, and sufficiently distant from 

 the influence of other celestial bodies, will perform revolutions round 

 a common centre of motion ; that hence they will always move in di- 

 rections opposite and parallel to each other ; and that their system, 

 if not destroyed by some foreign cause, will remain permanent. This 

 kind of rotation is exemplified by the instance of our earth and the 

 moon. Dr. Herschel proposes, on a future occasion, to communi- 

 cate a series of observations made on double stars, whereby it will 

 be seen that many of them have actually changed their situation with 

 regard to each other, in a progressive course, denoting a periodical 

 revolution round each other, and that the motion of some of them is 

 direct, while that of others is retrograde. 



3. More complicated sidereal systems, or treble, quadruple, and 

 multiple stars. From the combination of two stars, it is easy to ad- 

 vance a step further, and allow that three or more stars may be con- 

 nected in one mutual system of reciprocal attraction ; and the com- 

 putation for determining the common centre of their respective orbits 

 is here exemplified by a variety of hypothetical cases. The author 

 at the same time asserts, that there is not a single night when in 

 passing over the zones of the heavens by sweeping, he does not meet 

 with numerous collections of such multiple stars, apparently insu- 

 lated from other groups, and probably joined in some small sidereal 

 system of their own. 



4. Clustering stars. These are described as great collections of 

 small stars that are profusely scattered over the milky way, by no 

 means uniformly, but unequally dispersed in many separate allot- 

 ments. An instance of one of these aggregates is given, which in a 

 space of about 5 between /3 and y Cygni, contains above 331,000 

 stars. A more particular account of the milky way, we are pro- 

 mised, will be the subject of a future communication. 



5. Groups of stars. These differ from the preceding class by 

 being collections of closely, and almost equally compressed stars, of 

 any figure or outline ; and from the next following, by showing no 

 particular condensation that seems to point out any ideal centre of 

 attraction. 



6. Clusters of stars. These are generally round, and the compres- 

 sion of their stars indicates a gradual accumulation towards their 



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