RECENT ADVANCES IN SCIENCE 527 



may be proved in a comprehensive manner by making use of 

 affine collineations in space. On Pohlke's theorem see also 

 E. Kruppa (57). 



On curves and line-complexes, see T. Cohen (17), L. P. 

 Eisenhart (7, 8), F. Kolmel (15), H. R. Brahana (9), W. 

 Gaedecke (15), H. Mohrmann (16, 21, 25, 26, 28), S. Jolles 

 (18), J. Thomae (19), H. Falkenberg (22), H. Liebmann (25), 

 H. Beck (27), K. Fladt (28), J. de Vries (49), H. J. van Veen 

 (50), K. W. Rutgers (50), D. Postma (50), Gy. Nagy (55), 

 G/Kohn (56), A. Plamitz (56, 58, 59), H. Beck (58), H. Rothe 

 (59), P. Roth (60), L. Theisinger (60), E. Muller (61), K. 

 Mack (61), and L. Braude (62). 



On surfaces, G. M. Green (8) gathers together a few of 

 his more important results concerning the general theory of 

 curved surfaces and rectilinear congruences. On the genera- 

 tion of surfaces of the second order by correlations, see F. 

 London (16) ; on quadrics, see H. Lebesgue (37) ; on algebraic 

 surfaces, C. H. Sisam (37), F. Enriques (47) ; on infinitesimal 

 geometry of surfaces, Z. Geocze (54, two papers), C. Guichard 

 (33-4)> E. Turriere (38), A. F. Carpenter (46), S. W. Reaves 

 (47), E. Cartan (39), A. V. Backlund (64) ; on curves on ruled 

 surfaces, see C. Juel (11); on minimal surfaces, see J. K. 

 Whittemore (9), E. R. Neovius (n); on the rigidity of convex 

 polyhedra and other convex bodies, H. Weyl (12) ; theorems 

 on convex bodies, W. Blaschke and G. Hessenberg (16; cf. 

 Blaschke, 17); on Lie's transformation, M. Fouche (39); 

 see also E. Muller (58, 59), L. Zangl (59), P. Lehmann (59), 

 K. Zindler (61), and P. Roth (62). On gauche surfaces M. 

 d'Ocagne (35) and R. de Montessus de Ballore (36). 



ASTRONOMY. By H. Spencer Jones, M.A., B.Sc, Royal Observatory, 

 Greenwich. 



A New Theory of Jupiter's Satellites. — Prof. W. de Sitter has 

 published in the Annals of the Leiden Observatory, 12, part 1, 

 191 8, the outlines of an important new mathematical theory 

 of Jupiter's satellites. A much abridged summary is also given 

 in K. Akad. Amsterdam, Proc. 20, 1 289, 191 8. The principal diffi- 

 culty in the theory of the four old satellites of Jupiter arises 

 from the fact that the mean motions of the three inner satellites 

 are commensurable. The mean motion of the fourth satellite 

 is not commensurable with those of the others, and its theory 



