RECENT ADVANCES IN SCIENCE 15 



ruption occurs into two masses rotating about one another, the 

 ratio of the two masses being independent of the initial density 

 or momentum. 



The far more difficult problem of non-homogeneous and 

 compressible masses is then treated. The conclusion is reached 

 that the process of evolution is substantially the same as in 

 the previous case, and that the ultimate result is two detached 

 masses. This theory seems to have an obvious application 

 in binary stars, which are so numerous in all parts of the sky. 

 It is not easy, however, to test it in a decisive manner by means 

 of the observational evidence provided by such systems, although 

 the general agreement is satisfactory. A more decisive test is 

 provided by triple and multiple stars, and an examination of 

 the evidence leads to the conclusion that some such systems 

 can be explained by rotational disruption, whilst others cannot. 



The rotational theory was first put forward by Laplace to 

 explain the existence of the solar system. Mr. Jeans examines 

 whether such a system could be formed by any alternative 

 sequence of processes ; after trying various hypotheses he 

 reaches the very important conclusion that " unless some new 

 and at present unthought-of factor appears, we seem forced to 

 conclude that rotational theory cannot explain the genesis 

 of our solar system." The outstanding difficulty is the com- 

 parative absence of rotation. 



Further investigations show also that the rotational hypo- 

 thesis can account for the formation of spiral and possibly also 

 of ring nebulae, and that from it a reasonable scheme of cosmic 

 evolution can be evolved. Starting from the condensing, 

 irregular mass of gas, gradually acquiring rotation through 

 tidal forces raised by other masses, this may evolve through a 

 flattened shape into a spiral form, which may condense into 

 streams of stars such as are seen in the Andromeda nebula, 

 and then into a flat galaxy of stars which gradually becomes 

 successively spheroidal and then almost globular. But the 

 evolution of our own solar system still remains as great a 

 mystery as ever. 



Double Stars. — An important catalogue of double stars by 

 M. R. Jonckheere is published in Memoirs R.A.S. vol. lxi. 

 191 7. M. Jonckheere was director of the Observatory of the 

 University of Lille, and is a well-known double star observer. 

 During his exile in England he has completed the observations 



