132 ANNUAL EEPOET SMITHSONIAN INSTITUTION, 191-5. 



particles. According to the calculations of Chapman, the moon also 

 possesses this power in much less degree but nevertheless surely. To 

 it are due several oscillations the most marked of which has a period 

 of half a lunar day. 



We are not yet in the position for studying the distribution of 

 magnetism on the moon. But in lunar topography we are making- 

 progress. The valuable collection of plates collected at the Observa- 

 tory of Paris furnished the basis to Le Morvan of a new 4:8-plate 

 atlas of our satellite. One half of this work had appeared in 1913. 

 This chart, less expensive and more manageable than the great atlas 

 of this observatory, is well conceived, admirably executed, and will 

 be of great value to observers. 



The planetoid Eros, which so held the attention of astronomers in 

 1900, had at that time surprised them by its rapid variations in 

 brightness. Now we find that its orbit is contracting more than we 

 would have predicted. There will result far more favorable condi- 

 tions for a new determination of the solar parallax. In 1931 the dis- 

 tance of this planetoid from the earth Avill be decreased to almost one- 

 half of the smallest value reached in 1900. 



The system of planets which revolve about the sun, and the two 

 systems of moons which keep company with Jupiter and Saturn, re- 

 spectively, have always attracted calculators in a search for numerical 

 analogues. The well-known law of Bode serves as the point of de- 

 parture for such calculations, and its aspect is changed slightly, 

 according as weight is attached to the exactness of the verifications, 

 the absence of discontinuities, or the small number of parameters. 

 Miss Blagg has made a marked advance over her predecessors, includ- 

 ing the three series of distances in one formula, analogous to one 

 which connects the reciprocals of the wave-lengths in the spectra of 

 simple bodies. The existence of this relation between such apparently 

 different systems makes us feel that we are dealing with some mysteri- 

 ous physical law imposed in the formation of the planets as well as 

 of the satellites. Such grouping could not be the effect of fortui- 

 tous and successive aggregations, as the theory of capture would have. 

 It rather forces us to require in each system a unity of origin, retaining 

 the general idea of the cosmogony of Laplace. 



None of the laws derived from that of Bode would have foretold 

 the existence of the distant and retrograde moons which both Jupiter 

 and Saturn possess. In studying these two exceptional cases, Avhich 

 have been considered by certain authors as irreconcilable Avith the 

 ideas of Laplace, Jackson found that these anomalous moons, could 

 be considered as the remains of a nebulous ring, the component parts 

 of which possessed confused movements, and sufficiently vast to have 

 expanded beyond the sphere of effective attraction of the planets. 

 Certain distances from the planets and certain angular velocities are 



