Proctor's Astronomical Lcclur 



19 



Cnme tail a Ion? tall, 90,000,000 miles in ex- 

 tent, was seen, no longer carried b.>liiud 

 the comet, but traveling now in front of it ; 

 and in the day or two that that comet was lost sight of, 

 that long tail was tiro wn out by the retreating comet. 

 Now that comet had taken four weeks in approaching 

 the sun over a distance of 90,00r>,000 miles, though hav- 

 ing, at starting, all the velocity with which it had ar- 

 rived; but in less than four days that wondrous tail, 

 9XOTX),000 miles long, waa thrown out in frout of the 

 body. 



* * 



COMET OF 1630. 



There Is a fact which either shows us we have to deal, 

 us to a comet's tail, with matter which has not been 

 formed In reality, but is some wav made to become ap- 

 parent to us, or else we have to deal -with a force incom- 

 parably pi-eater than gravity. Tbis repulsive force of 

 ttio snn seems incomparably greater than that of grav- 

 ity. Gravity had led that comet over a distance of 

 50,000,000 miles in four weeks, and it threw out its tail in 

 four 'days. There is the first evidence 

 of this mighty repulsive force of t'ae sun. 

 The comet came so close to the sun a distance only 

 the 160th part of that which separates our earth from 

 the sun that the heat to -which it was exposed was 

 25.603 times greater than the heat endured by our earth. 

 There then was a heat which we might very well 

 imagine would destroy the very substance of our ele- 

 ments. ATI the materials on our earth -would, under 

 Burn nheat.be vaporizod. Newton assigned a path to 

 the comet of 1630, but was not able to assign a period 

 to It. Ha was not able to say for how lone a time 

 It would pa3 away before It returuert; but in the case of 

 Halley's comet. D.r. Halley not only calculated the path 

 the comet would follow, but he looted through the 

 annuls of astronomy to see if there were any comet 

 traveling on the same path. He found one in the 

 year 1607, and another In the year 1531, and 

 noticing ' that the interval from 1607 to 

 1682 was not very different from the interval between 

 1531 and 160776 years about he concluded that the 

 cotuet had a period of 76 years, and he boldly presented 

 the prediction that in the year 1759 that comet would 



return to our neighborhood. The prediction was an 

 exceedingly bold one, and it was the first time an 

 astronomer bad ever ventured to say a comet would 

 follow a certain path at any given time ; and there 

 was this Interesting circumstance about it, that when 

 that comet returned, the astronomer who predicted it 

 would long since have passed away. 



SUCCESSFUL PREDICTION OF A COMET'S RE-APPEARANCK. 



When 1759 came astronomers went over the calcula- 

 tion made by Dr. Hallos 1 , an 1 they found, from their 

 greater mathematical experience, how that comet might 

 be dealt with. They were able 10 tell the very month, 

 and even predict the day. They said upon April 13, 1759 

 with a limit of error of one month, this comet would 

 come back to its point of nearest approach to the sun. 

 It actually returned, and made its nearest approach to 

 the sun on March 13, 1759, or just within the limits of 

 error. They did not know at that time that the planets 

 Uranus or Neptune existed, and these had exerted their 

 influence on that comet. 



But when the return year 1835 was approaching, as- 

 tronomers had learued about Uranus, though Nep- 

 tune had not been discovered, and also how to 

 deal much more perfectly with the processes of 

 mathematical analysis involved in calculating 

 the course of celestial bodies; and they said this 

 comet would return in November, 1835, and they put the 

 dates between Nov. 12 and Nov. 16. A German astron- 

 omer, Rosenberger, gave the exact date as Nov. 13. The 

 exact date on which the comet did make its nearest ap- 

 proach to the sun was on Nov. 12, and certain strange 

 facts were noticed. As it approached the sun It pre- 

 sented a very remarkable head, which you recognize here 

 (picture shown), with a crescentic ridge of brightness. 



COMET OF 1835. 



II seemed as if it were forced from side to side by some 

 disturbing force exerted by the sun. That comet passed 

 around the sun, made its nearest approach, ap-1 came 

 around on the other side, passing southward There 

 fore it was observed by astronomers of the souther/ 



