The daily morning journal and courier., 1906-10-06
COMETS.


 What, then. do these various in, stances indicate? Surely very clearly that the nuclei of comets aresil gene ral collections or aggregates of meteor ties, which are easily broken up into smaller groups or gradually spread and dispersed along comets path until it may at last happen that the comet will be wholly dissipated and be seen no more. Tn any case dtnarafcal consider auons Indicate. that the n1eteorites most Lcontinue to travel very nearly in the comets orbit
 This hypothesis is confirmed by cases in which the nucleus in the head of a comet has actually appeared to under go division. In the comet of 161s 1t is recorded that the head was at flrstslik a planetary disk, but presently the. as- tronomer Cysatus saw it as a cluster ing group of starry points. The comets of Oloinda in 1860 and of Brooks-in 1889 broke into two parts, somewhat as,did Biela's. The nucleus of'thes great, conl- ct of 1882 gradually broke into four portions, each of which it is quiteycon- ceivable may some day form a. separate comet
 But it may be asked: If comets, are thus composed of aggregaions of me teorites, of what size may we suppose the meteorites to be? The answer is that their size will probably correspond with that of such meteorites as the earth is constantly encountering. | NNhoeo F-or,,a,,f1yy Fol t.ra,, it hnipc sometimes of few pounds in weight or occasionally attaining even to hum dredweights or tons, as is indicated by specimens found in sltu in certain lo- calities, although they may not actu- ally have been seen to fall But 1t is likely that the weight of by far the greater number may attain to only a grain or two, as is the case with most of those which traverse the earth's atmosphere in the form of shooting stars.
 A comets nucleus is therefore proba- bly, composed chiefly of stony frag- lments varying in size from that of the finest dust to that of rocks of consider able magnitude. At the same time por- lions of a more or less metallic coInpo- sition may be intermingled.
 Eruptions from the nucleus may take Iplace in any direction. But they occur, as might be expected most frequently toward the sun, because on that side lmost heat is received. When so erup- ted the matter sent forth is in general seen to be presently thrown back again lin a curved past the nucleus, so as to form a brilliant hollow envelope around lit. the nucleus being within that part, of Ithe envelope which is most curved and convex toward the sum- Several such envelopes, outlying each other, are sometimes seen, which have been Horned in succession from series of explosions, the matter projected having attained to different elevations above the nucleus before being turned back.
 These envelopes, produced in this lway from jets first of all emitted to- ward the sun, of course help to form the comets tail after they have passed back beyond the head A much smaller amount of ejected matter, probably of a different kind, is sometimes seen on the sunward side of the head, like Q tail pointing toward the sun, and has occasionally been termed the comets beard. But the tail proper frequently iof immense extensiod nan always of al- most inconceiyably light density, inva- riably points away from the sun; so that it even travels, in a sense, in front of the comet after the perfheHon passage has taken place and the comet has begun to recede from the sun again.
 All this very clearly indicates, as nearly all astronomers have long al- lowed, that some great repulsive force emanates from the sun. which drives away with enormous speed in the oppo- site direction any matter elected to- ward the sun from the comets nucleus after it has risen to certain eleva- tion; while the same force, if such matt ter is elected in any other direction from the nucleus, sooner or later turns it all, in like manner backward into the tail.-Nineteenth Century and Af- ter.