A HISTORY OF SCIENCE 



solid or liquid, but they must be independent. The 

 entire system of rings must, therefore, consist either 

 of a series of many concentric rings each moving with 

 its own velocity and having its own system of waves, 

 or else of a confused multitude of revolving particles 

 not arranged in rings and continually coming into 

 collision with one another. 



" Taking the first case, we found that in an indefinite 

 number of possible cases the mutual perturbations of 

 two rings, stable in themselves, might mount up in 

 time to a destructive magnitude, and that such cases 

 must continually occur in an extensive system like 

 that of Saturn, the only retarding cause being the ir- 

 regularity of the rings. 



" The result of long-continued disturbance was found 

 to be the spreading-out of the rings in breadth, the 

 outer rings pressing outward, while the inner rings 

 press inward. 



"The final result, therefore, of the mechanical 

 theory is that the only system of rings which can 

 exist is one composed of an indefinite number of un- 

 connected particles, revolving around the planet with 

 different velocities, according to their respective dis- 

 tances. These particles may be arranged in series of 

 narrow rings, or they may move through one another 

 irregularly. In the first case the destruction of the 

 system will be very slow, in the second case it will be 

 more rapid, but there may be a tendency towards ar- 

 rangement in narrow rings which may retard the 

 process. 



"We are not able to ascertain by observation the 

 constitution of the two outer divisions of the system 



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