CHAPTER II.
Altogether the most important circumstance in whatmay he called the history of the moon, is the partwhich she has played in assisting the progress ofmodem exact astronomy. It is not saying too muchto assert that if the earth had had no satellite the lawof gravitation' would never have been discovered. Nowindeed that the law has been established, we can seeamid the movements of the planets the clearest evi-dence respecting it,—insomuch that if we could con-ceive all that has been learned respecting the moonblotted out of memory, and the moon herself annihi-lated, astronomers would yet be able to demonstratethe law of gravity in the most complete manner. Butthis circumstance is solely due to the wonderful per-fection to which observational astronomy on the onehand, and mathematical research on the other, havebeen brought, since the law of gravitation was estab-lished, and through the establishment of that law. Itneeds but little acquaintance with the history ofNewton’s great discovery, to see that only the over-whelming evidence he was able to adduce from the