196 THE POPULAR SCIENCE MONTHLY. 



en its period at each return. The absorption of the comets of 1843 and 

 18S0 by the sun's gaseous envelope, at some time in the distant future, 

 is therefore by no means improbable. Such results are not known to 

 have occurred in historic times ; but, if the sun is gradually contract- 

 ing i n other words, if its diameter was once considerably greater than 

 at present any comet passing so near the center as that of 1880 would 

 have plunged so deeply into the sun's atmosphere as to be absorbed 

 into its mass. It is true, moreover, that, when the motion of a body is 

 arrested, such motion is converted into heat. If the earth were stopped 

 in its orbit, its fall upon the sun would produce an amount of heat 

 equal to that now radiated in ninety years. If the mass of the comet 

 be -^JLq that of the earth, the heat produced by the impact would 

 scarcely be equal to that now radiated in seven days ; or, if the com- 

 etary mass be only equal to that of a globe one hundred miles in di- 

 ameter, and of the same density as the earth, the additional amount 

 of heat would be less than that now supplied in a single hour. It 

 may further be remarked that the collision would be as likely to occur 

 on the hemisphere turned away from the earth as on that turned 

 toward us. 



But let us assume that the great southern comet of 1880 was in fact 

 a return of the comet of 1843, that its present period is about thirty- 

 seven years, and that in consequence of its passage through the outer- 

 most strata of the sun's atmosphere its period must be shortened more 

 and more until it falls upon the sun's surface. The solar atmosphere 

 is known to be very rare from the fact that matter thrown out by the 

 sun's eruptive force has been seen to ascend to a height of two hun- 

 dred thousand miles. The resistance which it would offer to the 

 comet's motion would therefore be slight, and in all probability sev- 

 eral centuries would elapse before the comet's course would be termi- 

 nated by its falling upon the sun. Instead, therefore, of a sudden 

 catastrophe, we should have a gradual dissolution of the comet ; por- 

 tions becoming absorbed by, or incorporated with, the solar atmos- 

 phere at each successive perihelion passage. The apprehension of 

 danger to the earth from a great and sudden increase of the sun's heat 

 is, therefore, without any reasonable foundation. 



It is due to Mr. Proctor to say that he did not designate the year 

 1 897, nor indeed any other, as that in which the comet would fall into 

 the sun, nor did he express the opinion that the collision would occur 

 at the cornet'^ next return. He merely remarks that, "if already the 

 comet experiences such resistance in passing through the corona when 

 at its nearest to the sun that its period undergoes a marked diminu- 

 tion, the effect must of necessity be increased at each return, and after 

 only a few, possibly one or two, circuits, the comet will be absorbed 

 by the sun." This statement, though perhaps incautiously expressed, 

 is very different from that attributed by unscientific readers to its 

 distinguished author. 



