PHILOSOPHICAL TRANSACTIONS. 523 



parts of Europe, he has nothing of his own observation, having attempted after 

 he heard of it to discover it several mornings, but without success : he there- 

 fore proceeds to the observations of the second, which he first mentions to have 

 been observed by himself the 17 th of December 1 680. On Dec. 16, in the 

 evening, he says, the length of its tail was about 70 degrees, its breadth in the 

 middle about 2, and at the upper end about 3 degrees, full like a rain-bow, 

 reddish, and a little bended towards the west ; it passed through the Eagle, the 

 Dart, and the left wing of the Swan, covering the southern star in the neck of 

 the Eagle. The 17th about 5 in the evening he discovered the head, of the 

 size of a star of the first magnitude, among those of Antinous. He now 

 viewed the head with a l^-foot telescope, and saw it differing both from stars 

 and planets, being a dusky light like a cloud, about the size of the moon, and 

 brighter in the middle than the extremes. From which he draws these con- 

 sequences ; first, that its blaze was transparent : Secondly, that the head is not 

 made up of small fixed stars, as Stellas Nebulosae are. Thirdly, that he sees no 

 reason to conclude it a planet, because sometimes no nucleus, sometimes many, 

 are seen, which sometimes divide, sometimes unite. 



Upon the whole he concludes, that the blaze or tail is made by the rays of 

 the sun passing through the head, which he conceives a clear solution of the 

 constant opposition of the blaze to the sun. 2. That these rays are received 

 and reflected to us by a matter more dense than the aether. 3. That the head 

 of the comet is not a star, they being too dense, but this thin enough to trans- 

 mit rays of the sun. 4. That yet the matter of the head reflects the rays, and 

 may be of the same nature with the blaze. 5. That the head is more dense 

 than the blaze for the most part, though sometimes otherwise, and that it is 

 liot necessary it should be round. 6. That it is not enough that the matter of 

 the head be transparent, but it must give a greater power to the rays trajected to 

 enlighten the parts behind it, since it is not observable that the parts before or 

 round about it are so well enlightened. 7- That there are divers convex parts 

 in the head, which make this conic union of the rays behind them, which make 

 the brighter parts of the blaze. 8. That to form a comet, there is only ne- 

 cessary a union of some denser parts of the other formed into convexities, and 

 these disposed into a convenient order; which he believes may as well be sup- 

 posed to be naturally effected by these celestial clouds, as the figure and posture 

 of the clouds; which make a parhelion or mock sun, is naturally produced in the 

 atmosphere : so that in fine he concludes, that as a mock sun is nothing but a 

 sublunary meteor, fitly formed and disposed to represent the figure of the sun; 

 so a comet is nothing else but a celestial meteor, whose convex parts of con^ 

 densed matter reflect the beams of the sun sufficient to make the appearance 



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