Proctor's Astronomical Lectures. 



21 



tbnfc wny had f righfened the people out of their wits. 

 I*. 1771, a hundred years ago, tickets were offered for 

 Rile purporting to be reserved seats in Paradise, and 

 people actually bought those tickets. [Laughter.] la 

 1833 they wore not quite so bad, but still they were much 

 frightened, and many unfortunate circumstances hap- 

 pened In Prance on account of that fact. They required 

 to lie told anrt then they were not comforted that the 

 mere fact that the comet passed the path of the earth, 

 would not interfere with the earth; that the pas- 

 sage across the path of the earth, would not 

 injure the path, for the path was not a material thing. 

 The people were frightened, and they were not certain 

 that astronomers had calculated the path so exactly 

 that there would be no collision. But that 

 passed away, and nothing more Wua heard 

 until 1846, and then the comet was found trav- 

 eling on its usual p.itli, and to the great astonishment of 

 astronomers it was announced that the comet had 

 divided into two parts, each having a distinct head and 

 nucleus. It was noticed bv Capt. Maury at the Observa- 

 tory at Washington; but strangely enough, on the night 

 \vheu he observed the comet had doubled, the 

 records of the German Obs( rvatory showed the 

 comet to be single, and it would appear, 

 therefore, that the greater clearness of the atrcos- 

 phere in America had enabled him to recognize 

 the chiinge before it was noticed in Europe. Two sepa- 

 rate comets traveled along, side by bide, and the strange 

 circumstance was noted that they interchanged light; 

 sometimes one and sometimes the other was brighter, 

 as if there were communication between them. They 

 were a kirn! of Siamesa twius. They passed into space, 

 and astronomers thought they could watch the comets 

 agiin and ascertain how they were separated, but the 

 comet was never seen again. The year 18GG cams around, 

 and astronomers calculated toe path of the comet. 

 They looked for it. Tney examined the path over the 

 Leavens a great distance on either side, but they failed to 

 recognize that comet. I told you that comet passed tlie 

 pitth of the earth, and there are other systems which 

 aUo cross the path of the earth. It wus suggested that 

 the comet had encountered meteor systems and split 

 up, and was again and again split up, and so vanished. 

 Yon will see there was an important connection between, 

 that and what we have learned since about the comet's 

 history. The year 1872 came, and that comet was again 

 looked for. Other calculations were made as to its path. 

 It was looked for more carefully, but in 1872 it was not 

 seen. I leav^ its history for the time, presently to re- 

 turn to it. 



WHY SOME TAILS ARE STRAIGHT AND OTHERS CURVED. 



There was a comet seen in 1858, and called Donati's 

 couiet* Here Is a picture of the comet as seen in En- 

 gland, and it looks like a plume, but in America thac 

 comet was observed to have not merely the plume- 

 ehnped body, bat also a perfectly straight tail, and in 

 Borne ^pictured two straight tails. Let us in the first 

 place, deal with that comet. Why should th tail of a 

 eomet be curved! The position of a comet' ail is due 

 to repulsive action, and if that rer e action 

 take place immediately, it is qui clear the 



tail will be swept into a straight -liuo; -and 

 if you looU at a straight Hue, no matter 

 how placed, it would look straight. But if the 

 process of repulsion takes place at a moderate 

 rate, the tail would appear curved. You can under- 

 stand that a curved tail b jhind a comet is due to repul- 

 sion not taking place instantaneously. Tue head of the 

 comet cousisis of two kinds of matter 0113 was repelled 

 with moderate velocity, very gre.it but moderate by 

 douiparison and the other repelled with great velorit^, 

 and so swept off into a straight line. It would be mani- 

 fest to you, that being tie case, since there was a sep- 

 aration of the matter in the comet's tail, that if tho 

 comet's head was complicated in structure, there would 

 De an intermixture of the two kinds of matter, 

 end the portion of the matter more readily repelled 

 would escape, carried off by the other tail, carried ofl 

 into the curved tail, and at last would be swept away ; 

 and perhaps a little later another portion would be 

 swept away, and so you would see extending from the 

 curved tail various streaks of this matter. Yoa have 

 here, a picture of tho curved tail, aud you will notice the 

 variety ot streaks thrown out from that thrown 

 straight out, indicating tho action of that kind of process 

 \ve have been describing. Matter more easily repelled 

 was carried away with tho matter less easily repelled, 

 aud from time to tluio soma pares were swept off, 

 so that there was a combing out of tho tail of the larger 

 part, while the straight tail rem lined perfectly distinct 

 all the while. There was a curious fact indeed ; and it 

 seemed to dispose of Tyndall'a theory that the tail of a 

 comet is not produced by repulsion, but a certain kind of 

 action produced behind a comet, an i bringing out as it 

 were from space cloud-liko matter. Here is a process 

 which seems perfectly to correspond with the theory of 

 repulsion, and it seems explicable in no other way. So 

 that there is some force in the theory of a repulsive 

 power exerted by the sun. 



EXPLANATION OP THE PLURALITY OF TAILS. 



I must remark at this point that we owe to Prof. New 

 ton of Yale College those views as to the formation and 

 behavior of that comet's tail. They occurred independ- 

 ently to Sir J. Herschel; but found a paper contain- 

 ing a complete account of all the phenomena of that tail 

 had been published many years before. Now let us con- 

 elder the way i.i which the head is formed. There is the 

 comet as it first appeared as a small rouu.1 object, not 

 more distinguished in appearance than tha comet of 1843. 

 In time the comet became lengthened, ;md then grew out 

 a tail. There was iu the first place the formation of 

 a crescent-shaped object, and from either side of that 

 object matter was thrown off. The tail became divided 

 behind the head. As time passed, all around the central 

 bright part of the head, matter was raised from the 

 head of the comet, even as Herschel had found mattei 

 was raised from H.tlley's comet; it was raised and then 

 condensed aud formed an envelope around the comet 

 Over our rain-clouds the vapor of water ia raised, and 

 the process of cloud formation takes place again, so thai 

 we see two layers of clouds; so alter a time we begin 

 to notice two envelopes were formed, and in face von 

 can see the third envelope beginning to be formed 



