ASTRONOMY AND METEOROLOGY. 379 



whole issue of nebulous matter from the nucleus far into the tail was 

 curiously grooved and striated. It was noticed that both the princi- 

 pal ray and the dark channels penetrated within the outline of the 

 curved tail, the latter being clearly separated from the principal ray, 

 even to the naked eye, by a dark cleft just above their intersection. 



" The telescopic phenomena, though interesting, did not present 

 equally strongly-defined features with those which characterized the 

 great comet of 1858. We should, perhaps, except from this remark 

 the structure of the cometary envelopes for a day or two after their 

 first emission from the nucleus. In this stage they were intersected 

 by jets of luminous matter projected from the nucleus, and these 

 limits were pretty clearly outlined. 



" On the 2d of July, portions of three were visible ; the inner one 

 showing a variety of details. In its outline and general aspect it was 

 like others which followed it, almost a fac-simile, on an enlarged scale, 

 of some of those exhibited by the great comet of 1858. They rapidly 

 faded, or were lost in the surrounding haze, and their places were filled 

 by new ones. Latterly, two, at most, could be seen at one time. It is 

 qmte important to remark that the successive envelopes resembled 

 their predecessors not only in their general aspect, but quite closely 

 in the details of their structure ; the luminous jets not issuing at ran- 

 dom from all points alike of the nucleus, but continuing to follow a 

 nearly similar course at each new discharge from its surface. 



" The most natural inference from this would seem to be that the 

 nucleus, if it rotates at all upon an axis, does so very slowly. The 

 nucleus was, throughout, brilliant, and, to appearance, solid, with a 

 diameter of from 2"to 3"" 



The investigation of the elements of this comet by Messrs. Safibrd 

 and Hall, of the Cambridge Observatory, gives the following results : 

 diameter of the nucleus, variously estimated at from one hundred and 

 fifty to three or four hundred miles. On July 2d, the breadth of the 

 head at the nucleus was 156,000 miles, the height of the inner en- 

 velope 11,500 miles, and the length of the tail about 15,000,000 miles. 



As already stated, Mr. Bond estimated the tail of the comet of 

 1861 as one hundred and six degrees in length. Father Sec c hi, the 

 well-known astronomer of Rome, however, estimated it at one hun- 

 dred and eighteen degrees in length, on the 30th of June. This is 

 the greatest length in arc on record. 1 



Dr. Pape, of Altona, has examined carefully the question whether 

 the earth was at any time within the tail of the comet, and concludes 



i The clearness of the atmosphere has much to do with estimating the length 

 of comets' tails. In a clear tropical sky the tail may be traced much farther than 

 in English and American skies. The apparent length of comets' tails, moreover, 

 by no means indicates anything of their real length, and it happens that those 

 which appear longest are much shorter than many which do not appear half as 

 long. This is due to the different distances which the comets hold with respect 

 to the earth. While the great comet of 1861 had a tail which stretched farther 

 across the heavens than any previous comet, its real length did not exceed 

 15,000,000 miles. The great comet of Douati, with a tail of only about half the 

 length in arc, was above 50,000,000 miles in length. The former comet was only 

 13,000,000 miles distant, while the latter was four times as remote, or about 

 50,000,000 distant. The great comets of 1080 and 1843 had tails of lengths of 

 90,000,000 and 180,000,000 miles respectively the tail of the latter comet being the 

 longest of any comet yet observed. Prof. C. W. Tuttle, 



