THE MESSENGERS OF THE GODS 271 



tiles ; the sun would be in one focus, and following out Kepler's 

 law, its radius vector would cover equal areas in equal times. 



The observations made from different points were carefully 

 examined ; the path of the orbit, so far as might be, was plotted ; 

 it answered in every way to Newton's anticipations it obeyed 

 a law of expectancy. Thereafter the mystery of the comets was 

 gone. From that time onward their paths and the date of their 

 return, should their paths be of such a shape as to bring them 

 back, was simply a matter of mathematical reckoning. Newton 

 found that the comet of 1680 moved in an orbit so near to a 

 parabola that its period was some hundreds of years at the 

 least. Later observations tended to indicate that its path 

 might be that of a very much drawn out ellipse. If this be 

 true, it will return in some three centuries, probably around 

 the year 2255. If this idea of its periodicity is correct, it had 

 appeared previously in 1106 and in 531 A.D. ; it would be the 

 same which bore Caesar to his resting-place among the gods. 



Newton was jiot the first to suspect that the comets might 

 move in orbits like planets. Kepler had so surmised. In his 

 day there came a very splendid comet, afterwards to acquire 

 an especial significance as the first of these apparitions whose 

 orbit was reckoned and its predicted return realised. In the 

 year 1618 there were three more. Kepler made a book about 

 them, speculating concerning their nature in his wild and un- 

 restrained way ; but in this as in so many others, coming 

 wondrously near to the truth. His master, Tycho, had been 

 deeply interested in the subject, had likewise written a book 

 upon them. It was Tycho, indeed, who first showed from 

 accurate observations that these apparitions are not generated 

 within the earth's atmosphere, as had so long been supposed, but 

 that they come from beyond the orbits of the planets. It was 

 his boast that by means of his observations he had destroyed 

 for ever the seven-and-seventy solid crystalline spheres which 

 the ancient imagination had invented to account for the move- 

 ments of the planets and the stars. 



Tycho did not see that they travel in orbits, but he held 

 firmly to the view that they were celestial and not terrestrial 

 bodies. Following him, Kepler accounted for their appearance 

 and disappearance by supposing that they moved in straight 

 lines ; having once passed near the earth, they would then 

 recede indefinitely into space. He did not seem to think it 



