298 PHYSICAL SCIENCE BK. vn 



another, disembodied power. Some will even be 

 found to call it blood, or heat. So far is the mind 

 from being clear on all other subjects that it is 

 still in search of itself. 



XXV 



1 WHY should we be surprised, then, that comets, so 

 rare a sight in the universe, are not embraced under 

 definite laws, or that their beginning and end are 

 not known, seeing that their return is at long 

 intervals ? It is not yet fifteen hundred years since 

 Greece 



Counted the number of the stars and named them every one. 



2 And there are many nations at the present hour 

 who merely know the face of the sky and do not 

 yet understand why the moon is obscured in an 

 eclipse. It is but recently indeed that science 

 brought home to ourselves certain knowledge on 

 the subject. The day will yet come when the 

 progress of research through long ages will reveal 

 to sight the mysteries of nature that are now 

 concealed. A single lifetime, though it were 

 wholly devoted to the study of the sky, does not 

 suffice for the investigation of problems of such 

 complexity. And then we never make a fair 

 division of the few brief years of life as between 

 study and vice. It must, therefore, require long 



3 successive ages to unfold all. The day will yet 

 come when posterity will be amazed that we 

 remained ignorant of things that will to them seem 

 so plain. The five planets are constantly thrusting 

 themselves on our notice ; they meet us in all the 

 different quarters of the sky with a positive challenge 

 to our curiosity. Yet it is but lately we have begun 



