380 ANNUAL OF SCIENTIFIC DISCOVERY. 



that at its nearest approach we were about 2,400,000 miles distant 

 from its nearest edge, on the morning of June 29th at 2h. 24m. 



The above calculations of Pape, says Mr. Bond, in commenting on 

 the above inference, relate to the straight bright ray, which formed 

 the main tail of the comet. But there was, however, in addition, a 

 great mass of diffuse light, which separated from the ray, and swept 

 off towards Corona Borealis in the early part of July, reaching on 

 the 4th to a distance of 40 from the nucleus, and having a breadth 

 of 12 or 15. This would have barely grazed the earth on the 30th 

 of June. In a late number of the Bulletin of the Imperial Observa- 

 tory, at Paris, Mr. Hind suggests that a peculiar illumination of the 

 sky, noticed in England on that date, was possibly " attributable to 

 the commingling of the matter forming the tail of the comet with the 

 earth's atmosphere." The observations on this day have a peculiar 

 interest, from the fact that, at about lOh. mean time, Greenwich, the 

 earth passed the plane of the comet's orbit, and the outline of the tail 

 presented to us was that of the section formed by a plane perpendic- 

 ular to its orbit. 



The orbit of the comet of 1861, according to Mr. Bond, is undoubt- 

 edly that of a parabola. It has, therefore, in all probability, never 

 before visited the solar system, and will probably never return to it. 

 Its orbit, moreover, was nearly perpendicular to the plane of the 

 ecliptic, while those of periodical comets usually form a very small 

 angle with that plane. According to M. Leverrier, this comet differs 

 in many respects from any that have been hitherto observed. M. 

 Chacornac, who studied the nucleus of this comet with a powerful 

 telescope, states " that, instead of its being hollow, like the half of an 

 egg-shell, like most of the comets already observed, it presented the 

 appearance of a sun composed of fire-works, the bent rays of which 

 burned in the same sense." 



The attempts made to photograph the comet of 1861 were, without 

 exception, failures. Mr. Whipple, the photographic artist of Boston, 

 who, in connection with Mr. Bond, of Cambridge, successfully pho- 

 tographed Donati's comet of 1858, found that the comet of 1861 

 hardly made an impression on the most sensitive photographic sur- 

 faces. Mr. De la Rue, of London, also reports a similar result. He 

 found that an exposure of the sensitive plate to its luminous image in 

 a telescope for one hundred and twenty times as long as sufficed to 

 depict the comet of 1858, entirely failed in giving any trace of an 

 image : the contiguous fixed stars at the same time leaving upon 

 the plate a strong impression. These facts would seem to prove that 

 there was an essential difference between the comet of Donati and 

 that of 1861, in physical constitution, inasmuch as, whilst the lumi- 

 nous rays emitted by them were of almost equal intensities, the actinic 

 rays were almost entirely absent in the light from the latter. 



Polarization of the Light of the Comet of 1861. Father Secchi, 

 of Rome, who examined the comet of 1861 with a polarizing appara- 

 tus, with a view of determining whether the body was self-luminous 

 or shone only by reflected light, states that on the 30th of June the 

 polarization of the light of the tail, and of the rays near the nucleus, 

 was very strong, and could be distinguished by the polarise ope in 

 bands, while the nucleus itself presented no traces of polarization, 



