HUXLEY'S AMERICAN LECTURES. -jog 



lite is 2,000 times greater than that of the sun or moon as seen from 

 the earth. 



Periods of the Satellites. Prof. Newcomb gives 30'' and 14"" 

 as the pei-iod of the outer satellite, and V'' and 38"" as that of the 

 inner. Both move, like our moon, from west to east. The period of 

 the inner is less, while that of the outer is greater^ than a Martial day. 

 It is obvious, therefore, that, as seen from the surface of the planet, 

 the apparent motion of the satellites will be in opposite directions, 

 the inner rising in the west and setting in the east ; the outer rising 

 in the east and setting in the west so that the phenomenon of two 

 moons meeting in mid-heaven will be to the Martialists no unusual 

 occurrence. 



The Mass of Mars. Before the discovery of these satellites the 

 determination of the mass of Mars was a problem of great difficulty, 

 the body being too small to have much eifect in disturbing the mo- 

 tions of other planets. The value assigned by Burckhardt was 

 5TT5T5 *^^* ^^ *^^ ^^^ being unity. The difficulty of the problem 

 is now happily removed, and Newcomb has found from the elements 

 of the exterior satellite a value of -jo^wfo j ^ mass less than Burck- 

 hardt's in the ratio of six to seven. 



The Bearing of the Discovery on the Nebular Hypothesis. 

 The inner satellite of Mars completes three orbital revolutions in less 

 than a Martial day. This anomalous fact in the planetary system 

 would seem, at first view, to be utterly inconsistent with the nebular 

 hypothesis. The question is one of more than ordinary interest, but 

 its discussion may well be deferred until we shall have obtained more 

 exact information in regard to the Martial system. 



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HUXLEY'S AMEEICA:Nr LECTUKES. 



By Peofessob E. EAT LANKESTEE. 



THE five addresses which have been recently brought out by Prof. 

 Huxley in the form of a small volume were delivered under very 

 varied conditions, and deal with subjects widely separate from one 

 another. Three of them form a series of lectures on the doctrine of 

 Evolution, and were delivered by the author at New York in Septem- 

 ber, last year. These were the only popular scientific lectures which 

 Prof Huxley would allow himself to undertake during his summer 

 holiday devoted to a tour in tlie United States. The "Address on 

 University Education " was delivered at the formal opening of the 

 Johns Hopkins University, at Baltimore, during the same visit. The 

 concluding lecture of the present volume was delivered in connection 



