280 PHYSICAL SCIENCE BK. vn 



of us will believe that either the moon or the five 

 planets are carried by the wind or spun round 

 3 by the whirlwind. I trow not. And why ? Just 

 because they have not an irregular and unrestrained 

 motion. Let us apply the principle to comets. 

 They do not move in confusion or irregularity so as 

 to justify the belief that they are impelled by unruly 

 and fickle forces. Besides, even if those eddies 

 could enclose moist earthy elements, and had power 

 to raise them from the depths to the heights, 

 still they could not carry them up higher than the 

 moon. All their force is spent when they reach 

 the region of clouds. But as for the comets, we 

 see them sailing through the upper regions, mingling 

 with the very stars. It is, therefore, improbable 

 that a whirlwind could persist over such a long 

 distance, for the greater it is, the more rapidly is it 

 spent. 



IX 



1 LET Epigenes, therefore, make his choice of the 

 two alternatives : if the force is small, it cannot 

 reach so high ; if it is great and violent, it will the 

 more quickly break up. But further, according to 

 the opinion of people like Epigenes, these lower 

 comets do not mount higher because they have 

 too much earthiness in them. Their weight keeps 

 them in the neighbourhood of earth. And yet 

 these other comets, which are higher and last 

 longer, must have a more abundant material. For 

 they could not last so long were their supplies not 



2 replenished from a larger stock. I said a moment 

 ago that the whirlwind s eddy could not long endure, 

 nor could it mount higher than the moon, or as far 



