Notes on Star-Streams. 9 



From the northern part of the Milky Way there will be noticed 

 a projection towards the north pole from the head of Cepheus. 

 This projection seems to merge itself in a complex convolution 

 of stars forming the ancient constellation Draco, which doubt- 

 less included the ancient (but probably less ancient) constella- 

 tion Ursa Minor. After following the convolutions of Draco, 

 we reach the bright stars Alwaid and Etanin (/3 and 7) of this 

 constellation, and thence the stream passes to Lyra, where it 

 seems to divide into two, one passing through Hercules, the 

 other along Aquila, and curving upwards (see Fig. 1) into the 

 remarkable group Delphinus. 



The streams here considered, include every conspicuous 

 star in the heavens. But the question will at once suggest 

 itself, whether we have not been following a merely fanciful 

 scheme, whether all these apparent streams might not very well 

 be supposed to result from mere accident. Now, from experi- 

 ments I have made, I am inclined to believe that in any chance 

 distribution of points over a surface, the chance against the 

 occurrence of a sino-le stream so marked as that which lies 

 (in part) along the back of Grus, or (to take one within our 

 figure) as the curved stream of bright stars along Scorpio, is 

 very great indeed. I am certain that the occurrence of many 

 such streams is altogether improbable. And wherever one 

 observes a tendency to stream- formation in objects apparently 

 distributed wholly by chance, one is led to suspect, and thence 

 often to detect the operation of law. I will take an illustration, 

 very homely perhaps, but which will serve admirably to explain 

 my meaning. In soapy water, left in a basin after washing, 

 there will often be noticed a tendency to the formation of spiral 

 whorls on the surface. In other cases there may be no spirality, 

 but still a tendency to stream-formation. Now, in this case, it 

 is easy to see, that the curved bottom of the basin has assisted 

 to generate streams in the water, either circulating in one 

 direction, or opposing and modifying each other's effects, 

 according to the accidental character of the disturbance given 

 to the water in the process of washing.* Here, of course, 

 there can be no doubt of the cause of the observed pheno- 

 mena; and I believe that in every case in which even a 

 single marked stream is seen in any congeries of spots or 

 points, a little consideration will suggest a regulating cause 

 to which the peculiarity may be referred. 



It is hardly necessary to say that, if the stream-formation 



* Sometimes, a singular regularity of curvature is noticed, and a spiral is 

 formed closely resembling in configuration some of the great spiral nebula?, as drawn 

 by Lord Rosse, so that one is tempted to see in the centrifugal tendency of the 

 disturbed water, and the centripetal effects caused by reflection from the basin's 

 surface, causes which may in some sense illustrate the laws operating in wider 

 domains of space. 



