TWEXTY-SETENTH ANNUAL MEETING. 95 



moon's surface in the direction of the earth, and at the same time another 

 would be formed on the opposite side of the moon. As the lunar body cooled, 

 in the lapse of ages, there would result an elongated rigid mass, having its 

 longest axis pointing always towards the earth. As long as the moon re- 

 mained in the liquid or gaseous state, but contracting, and therefore increas- 

 ing her distance from the earth, the trend towards a fixed and final shape 

 and fixed periods of rotation and revolution would be very evident. "The 

 evidence for the efficiency in bringing about the actual configuration of the 

 lunar-terrestial system" is not weakened by any contrary hypothesis. 



Accepting all of the foregoing with regard to the moon, namely, that mil- 

 lions of years ago our satellite was in a liquid, or viscous, or gaseous condi- 

 tion; that its surface was swept by immense tides produced by the earth's 

 attraction; that its longest axis was made to point always towards the earth; 

 and that the rotation period and revolution period were forced into coin- 

 cidence; let us see whether the same things are true of other bodies in the 

 solar system. 



The discovery of Schiaparelli has made known the fact that Mercury and 

 Venus sustain the same relation to the sun that our moon does to the earth. 

 The close proximity of these planets to the sun when they were in a gaseous 

 state, and the tremendous tidal action of the sun upon their masses, shaped 

 their destiny. But, passing to the earth, a different order of things, that is, 

 a different law, must have been in operation. Our planet turns in one year 

 its entire surface to the sun; her rotation period is not synchronous with 

 that of her period of revolution; and her longest axis does not point toward 

 the sun. Somewhere, then, between Venus and the earth, is the dividing line 

 outside of which the sun's power is so much diminished that earth and all the 

 other outer planets, have their periods of rotation and revolution, none coin- 

 cident, and their entire surfaces are exposed at some time in their respective 

 revolutions to the sun's rays. . 



But how is it as to the satellites themselves? We know the condition of 

 our moon and her relation to the earth. 



In 1877, Mars was discovered to have two satellites, the outer one at a dis- 

 tance of 14,600 miles from the center of the planet, and the inner distant only 

 5,800 miles. Now, these distances are in comparison less than the distance 

 of our moon from the earth, and the satellites themselves being acted upon 

 to a less degree, on account of distance, by the solar attractive power, are 

 controlled by the comparatively nearer and therefore greater power of Mars. 

 The fact, too, that the diameter of the larger or inner satellite does not exceed 

 16 miles, and that of the outer 14 miles, makes it more than probable that the 

 Martial tide-raising power exerted upon these little bodies must compel their 

 rotation and revolution periods to coincide, and their longest axes to be 

 directed towards Mars himself. 



The action of the satellites of Mars upon each other may to some extent 

 modify the relations between the periods of rotation and revolution, but 

 owing to their proximity to their primary and his great size as contrasted with 

 theirs, this modification must be dwarfed into insignificance. 



Let us now pass to the consideration of the satellites of Jupiter. In the 

 November number of Astronomy and Astro-Phj^sics, appears an article "On 

 Recent Observations of the Satellites of Jupiter," by W. H. Pickering, of 

 the Lowell observatory, Arizona. From that article I quote the following: 

 "As it would seem that some astronomers are still doubtful about the accuracy 

 of my observations made upon these bodies (Jupiter's satellites) in 1892, I will 



