H ALLEY'S COMET 



J 3 



Halley's Comet in the Year 1682. 



sun's corona. At the appearance of the 1882 member, it was fully be- 

 lieved by some prominent astronomers to be the same comet which 



had appeared in 1843, which was 



being rapidly drawn into the sun 



by the resistance encountered at 



perihelion passage. It appeared, 



however, that the orbit, derived 



exclusively from observations after 



that event, indicated a period of six 



hundred or seven hundred years, at 



least thus disposing of the question 



of identity. The behavior of the 



body itself was, however, very sug- 

 gestive as to the true condition of 



things. After the close approach to 



the sun with its tremendous tidal 



strain, the nucleus was found to be 



broken up into a number of pieces. 



These parts, instead of approaching 



each other, separated more and more 



as long as the body could be kept in 



sight. At the next return, after some 



six hundred or seven hundred years, there will, no doubt, be four or five 



separate comets, following each other at intervals of perhaps a number 



of years. 



Halley confidently predicted the 

 return of his comet in 1759. He 

 also identified it as having been seen 

 in 1305, 1380 and 1456. The dif- 

 ference of period, which amounted 

 to one year and three months, was 

 somewhat disturbing, but Halley 

 assigned this to the true cause, 

 namely, the perturbations produced 

 by Jupiter and Saturn. He re- 

 marked that the period of the planet 

 Saturn might vary as much as a 

 month from the action of Jupiter. 

 He says : 



How much more liable to derange- 

 ment, then, is a comet, whose excursion 

 into space is four times greater than 

 that of Saturn, and whose orbit is so 

 eccentric that if the velocity be increased 



the l/120th of its value, the ellipse described the comet would be changed into 



a parabola. 



IIali.ey's Comet in the Year 1759. 



