1886.] NEW YORK ACADEMY OF SCIENCES. 249 



We mention in passing, but without indorsement, tlie specu- 

 lations of Houzeau, who has attenijitecl to account for some of 

 the older observations of a satellite to Venus, by supposing 

 another smaller sister planet, " Neith," circling around the 

 sun in an orbit a little larger than tiiat of Venus, and from time 

 to time coming into conjunction with it. But the theory is 

 certainly untenable; a planet large enough to sliow phases, as 

 the hypothetical satellite is said to have done, in the feeble tele- 

 scopes with wiiich many of the observations were made one hun- 

 dred years ago or more, would be easily visible to the naked eye 

 even. There can be little doubt that all the Venus satellites so 

 far observed are simply ghosts due to reflections between the 

 lenses of the telescope, or between the cornea of the eye and the 

 eye lens. 



Ma7's. 



But while Venus has gained no moons during the past ten 

 years. Mars has acquired two, and they are .both native Ameri- 

 cans. There is no need to recount the faithful work of Profes- 

 sor Hall with the then new great telescope at Washington and 

 its brilliant result; brilliant in a scientific sense, that is, for 

 regarded as luminaries, it must be admitted that the Martial 

 satellites, in spite of their formidable names of Phobos and 

 Deimos, do not amount to much. Under the best of circum- 

 stances, they are too faint to be seen by any but keen eyes at the 

 end of great telescopes. Small as they are, however, the little 

 creatures punctually pursue the orbits which Hall has computed 

 for them, and, when the planet came to its opposition a few 

 weeks ago, they were found just in their predicted places. They 

 are interesting, too, from the light they throw upon the genesis 

 and evolution of the planetary system, almost compelling the 

 belief that they have come gradually into their present relation 

 to the planet. The inner one, Phobos, revolves around the 

 primary in 7h. 39m. which is less than one-third of the planet's 

 day. The theory of "tidal evolution" proposed by Prof. G. H. 

 Darwin in 1878-80, as the result of his investigations upon the 

 necessary mechanical consequence of the tidal reactions between 

 tlie earth, sun, and moon will account for Phobos, and I know 

 nothing else that will, though, of course, it would be rash to 

 assert that no other account can ever be given. 



Much attention has also been paid to the study of the 

 planet's surface. In 1876 we were already in possession of 

 three elaborate maps, by Proctor, Kaiser, and Terby, agree- 

 ing in the main as to all the characteristic formations. In 1877, 

 Schiaparelli, of Milan, detected, or thought he did, on the 

 planet's surface a numerous system of " canals " — long, straight. 



