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Astronomy.

th 3

4. These Tails also are so fine and tranflucid> ^

the Stars are distinctly visible through them. 'fteibrife from the Head and ascend, they become rar i f uiand grow broader towards the upper End. The ^of the Tail is well known to all now living .fy 3the late Comet; in which we observe the Ta>lsmall Flexure or Curvature, as they all liavs, jjjchconvex on the anterior Part, and concave behind .arises from the twofold Motion of the Particles 0 ^ctTail, the one of the Ascent from the Head, £ h® sti'being the progressive Motion in common with th soclem itself. But as the former is much the g rca£e j (°its Direction is but little alter'd by the latter, athe Position of the Tail but a little oblique and !l1vated. et3 ff

5. As to the Cause of the Ascent of the

Vapour or Tail towards the Parts opposite to the ^there have been various Surmises and Conjectn/® 1 ’’ ,,Jso I call them, as not being attended with Certains t jiCDemonstration. Kepler ascribes it to the Acti° n ..

Sun’s Rays rapidly carrying the Matter of the T al ))t t#with them, And Sir Isaac does not think it difl' 0l l a c e 5Reason, to suppose the subtil Æther in those h®®

/ may yield to the Action and Direction of the Sun- c0 V

It is certain from Experiments, that the Solar R a Llected by a Burning-Glass to a Focus, impel Tigpendulous Bodies very notably, even so as tom^ s,ifVibrate backwards and forwards : And though 1 ^ S Jyp'pulston of the Rays of Light with us, in our g r ° u\e ’>diums, and on our sluggish Matter, be iiiconh® o f >yet in those free Spaces, and on the subtil Ey* a y V 'line Particles of the Cometary Atmosphere, i £very great. I know there are other and 1 ate ^ 0l ri et 5theses to account for the Motion and Form of aTail; but on Examination they appear to ^ c heJ -e(° (6cient, improbable, and unphilofophical, and tshall not trouble the Reader with them. ,

6. The Bodies of Comets are very small, an pslthe Orbit of the Moon, as is evident from

they have no perceptible horizontal ot dhtrnal 1 ^pirand when view’d with a Telescope at their near6 j I1 g t ^tances appear less than to the naked Eye, by ^^plen^