1902.] on the Nebular Theory. 161 



movements of revolution and movements of rotation in tlie solar 

 system had a common direction. The mathematical mind of Laplace 

 drew a remarkable inference from this unanimity. Here, he said, 

 are thirty different movements; each of them might have been either 

 from right to left or from left to right, but, as a matter of fact, they 

 are all unanimous. Laplace showed that there was a thousand mil- 

 lions to one in favour of this unanimity being the result of some 

 common cause, and the nebular theory offered such a cause. For as 

 the great nebula was rotating it carried round with it, of course, the 

 masses of nebulae which were ultimately to form the planets. As 

 each of the planets broke away from the central mass it was found to 

 be revolving, just as the Moon revolves round the Earth, as the 

 mass contracted further, its motion accelerated anl the planet came 

 to turn more quickly on its axis, though still at all times revolving 

 in the same direction. In this way the unanimity of the movements 

 was a natural consequence of the Nebular Theory, and no other method 

 has ever been suggested by which so remarkable a concord could have 

 arisen. Laplace deemed that the thirty common movements were 

 sufficient to establish his argument. 



But the modern discoveries have enormously strengthened the 

 original argument. There are now 600 objects which revolve around 

 the Sun, and they all move in the same direction. The numerical 

 expression for the probability of the truth of the Nebular Theory has 

 to be correspondingly amended. The argument has been strength- 

 ened billions of times. 



The attention of astronomers at this moment is directed to the 

 marvellous nebula associated with the new star in Perseus. Photo- 

 graphs taken at the Yerkes Observatory show that the nebula is in 

 a state of rapid motion. This remarkable announcement has been 

 confirmed by a similar series of photographs taken at the Lick 

 Observatory. Such a discovery would be of interest were it only 

 for the circumstance that it is the first occasion on which motion in 

 a nebula has been certainly observed. But the most important 

 circumstance is the extraordinarily high velocity of the motion. 

 Nothing is known of the parallax of this star, except that it is too 

 small to be appreciable, we cannot therefore state exactly to what its 

 velocity amounts. It seems that it must be at least twenty thousand 

 miles a second, but it may be even ten times as much. 



Whether the phenomenon is velocity of actual matter, or whether 

 the observations may not admit of some other explanation, must for 

 the present remain undetermined. 



In a notable lecture which Huxley gave in the year 1880 on the 

 coming of age of ' The Origin of Species,' he mentioned some great 

 discoveries in Geology and Biology which had taken place since the 

 publication of the immortal work. He then announced that these 

 fresh discoveries brought such wonderful corroboration and illustra- 

 tion of the truth of Darwin's theory that if the famous doctrine of 

 natural selection had not been formed to account for the facts of 



Vol. XVIL (No. 96.) m 



