TWENTY-f^mEyTH ANNUAL MEETIXd. <)7 



(a) The sun, at a distance of 67,000,000 miles from the planet Venus, and 

 with a mass 425,000 times as great as that of the planet, has, according to 

 Schiaparelli, forced the rotation and revolution periods of the planet to be 

 coincident. 



(b) Beyond Venus, away from the sun, the latter body fails to produce a 

 like result upon the other planets. 



(c) The earth is 238,000 miles from her satellite, has a mass 81 times as 

 great, and the two periods are coincident. 



(d) Jupiter's first and second satellites are in the same relation to their 

 primary that our moon is to the earth. 



Jupiter is 1,167,000 miles from his outer satellite, has a mass 42,480,000 

 times as great, and has given to the satellite an elongated or ellipsoidal form, 

 a result of the tremendous pull of the planet upon the former plastic con- 

 dition of the satellite. It must follow that No. 4 has motions just as the first 

 and second have, and always shows the same face to the primary. 



(e) The distance, mass, and gravitation relations of the third and fifth 

 Jovian satellites, and of all the moons of Saturn, Uranus, and Neptune, being 

 substantially the same as those of our moon, it is safe to say that their rota- 

 tion and revolution periods are coincident, and they never show but one face 

 to their primaries. 



Whatever we may think as to the moon's past, and however long we may 

 suppose her period of rotation to have been when she started on her career 

 as an independent body, the fact that she turns the same face constantly 

 towards us, tells us of long stretches of time, in her history, that must be 

 measured by millions of years. And upon the hypothesis that millions, and 

 perhaps tens of millions, of years ago, the moon was a mass of liquid or gas- 

 eous matter, and that in this condition, she was exposed during all those ages 

 to the earth's pull or attraction, it can be easily seen that the period of her 

 rotation and that of her revolution would be gradually forced into coincidence. 



And so, when we consider the facts already established concerning all the 

 satellites of our system, as well as those pertaining to the movements of the 

 planets Mercury and Venus; when we consider the law of gravitation, the 

 masses and the distances of all these bodies; and, further, when we under- 

 stand the meaning of the observations of Schiaparelli and Pickering, we 

 must conclude that the modern theory of "tidal friction" when applied to 

 the satellites, is true. 



