third case, that is of the swift rivulet, we shall see the 

 main mass rolling quickly on the current while, behind, 

 a conical tail of more or less scattered particles is quickly 

 formed. A similar process takes place with our comets 

 Falling into the cosmic tide, as dead matter destitute of 

 organs of movement, they float in space in spherical form 

 until they drop into that network of moving gases which 

 we described. If their direction is towards the centre 

 they preserve their oval rounded shape till they reach 

 the sun. but if they touch the edges or the sides of this 

 gaseous basket, they are drawn out in the shape of 

 rockets with a longer or a shorter tail, according to the 

 place of contact. 



So in reality it proves. The comet first appears 

 through the telescope in the shape of a round spot, and 

 a marked change becomes observable when it attains the 

 perihelion. 



Comets occupy a space in the solar system which, 

 thoug large, is still insignificant in comparison with pla- 

 netary clouds. I shall dwell upon these planetary clouds, 

 in order to show their connection not with protoplastic 

 but with dissolving worlds. 



Planetary cloudspots are those which have the appear- 

 ance of a star or planet. They emit a feeble bluish 

 light, and some of them can be seen by the^naked eye, 

 whilst others can hardly be detected even with the help 

 of large refractors. Their bulk is sometimes very great, 

 and their shape most erratic. For instance the cloud- 

 spot in the constellation of Orion, is several thousand 

 times larger than our whole solar system, and in one 

 part resembles the open jaws of a wild beast. The 

 clouds in some constellations have a spiral conformation ; 

 in the constellation of the Calf we observe a crablike 

 shape ; in Andromeda a disc ; in the Dragon a net. 



But for us not their form but their substance is im- 

 portant. The fact that on examination of these cloud- 

 masses the telescope revealed in cases the presence of 

 globular starry worlds, caused astronomers to assume 



