RECENT ADVANCES IN SCIENCE 23 



applications of the method to stellar clusters may be made. 

 (4) Another important application is the photometry of comets. 

 If sufficiently accurate measurements can be made, it will be 

 possible to determine whether the effect of radiation pressure 

 is sufficient to cause any deviation from the inverse square 

 law and also to determine comets' masses. (5) The accurate 

 photometry of the planets relative to fixed stars will enable 

 any variation in the sun's brightness to be determined. Hence 

 the question as to whether or not the sun is a variable star 

 could be cleared up. In order to distinguish between solar 

 variability and a change of the planet's albedo it would be 

 necessary to observe regularly at least two planets. (6) By 

 making measurements on a part of the moon's surface not 

 directly illuminated by the sun, the albedo of the earth could 

 be determined, which is of considerable importance for meteor- 

 ology. (7) Many solar phenomena lend themselves to photo- 

 metry by this method, such as the brightness of the corona 

 or of solar protuberances and faculse. 



Various other possible applications are touched upon in 

 the paper, but the above will suffice to indicate that the 

 method is one possessing great possibilities, and which should 

 provide very valuable information on many important matters. 

 Unfortunately, it is not at present possible to obtain the cells 

 or a sufficiently sensitive electrometer commercially in this 

 country, and until this drawback is remedied the use of the 

 method is likely to be considerably restricted. 



The following is a selection of the more important papers 

 which have recently appeared : 



Historical. Fotheringham, J. K., The New Star of Hipparchus and the Dates 



of Birth and Accession of Mithridates, M.N., R.A.S. 79, 162, 1919. 

 Dreyer, J. L. E., The Place of Tycho Brahe in the History of Astronomy, 



Scientia, 25, March 19 19. 

 Dynamical Astronomy. Block, H. G., Sur une equation differentielle du 



probleme de la rotation des corps celestes, Ark. for Mat. Ast. och Fys. 



14, No. 3, 1918. 

 Spacer, V., Uber den Einfluss der Kriimmung der Erdoberflache und der 



Schwerkraftsanderungen auf die Pendelbewegung, Ast. Nach. No. 4974, 



1918. 

 Bosler, J., L'Influence des meteorites sur l'excentricite de l'orbite terrestre, 



Bull. Astr. 35, 242, 1919. 

 Stroobant, P., La Constitution de l'anneau des petites planetes (2 me partie). 



Ann. de P Observatoire royal de Belgique, 14, 19 18. 

 LAGRULA, J., Procede de calcul rapide de l'orientation du grande cercle de 



recherche des asteroids, Bull. Astr. 35, 228, 1919. 



