A dissertation on comets, extracted from the writings of the most eminent modern astronomers and philosophers. In a letter to a reverend professor. To which is prefixed the theory of a comet / by [according to the sentiments of] Sir Isaac Newton [and other ... astronomers].

Date:
[between 1700 and 1799]
Catalogue details

Licence: Public Domain Mark

Credit: A dissertation on comets, extracted from the writings of the most eminent modern astronomers and philosophers. In a letter to a reverend professor. To which is prefixed the theory of a comet / by [according to the sentiments of] Sir Isaac Newton [and other ... astronomers]. Source: Wellcome Collection.

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    folar Region ; becaufe their Heads, being then moll intenfely heated, emit the greateft Quantity of Vapours. Sixthly, Their Tails always decline from their Oppofition to the Sun into thofe Parts, which their Heads leave as they proceed in their Orbits. Of which the Reafon is, that all Smoke, or Vapours, ifluing from a Body in Motion, afcends obliquely, Hill receding Part, in which the emitting Body 7y, That the Deflexion or Declina¬ tion, ceteris paribus, is lefs when the Head approaches nearer the Sun, and alfo lefs near the Head of the Comet, than at the Extremity of the Tail: Becaufe the Vapour afcends more fwiftly near the Head of the Comet, than at the Extremity of the Tail; and when the Comet is lefs remote from the Sun, than when more. Eighthly, The Tails in their convex Part are fomewhat more fplendid, and diflindtly terminated, than in their concave Part; be¬ caufe the Vapour in the fwelling Part that proceeds, being fomewhat fuller and thicker, reflects the Light more copioufly. Ninthly, The Tails, at their upper Ex¬ tremity, always feem broader than near the Plead of the Comet. The Reafon of which is, that a Vapour, in open Space, continually rarifies and dilates. tfenthly, The Tails are tranfparent, and even the fmalleft Stars are feen thro* them ; becaufe the Vapours, of which they conlift, are extremely thin. Thefe are the chief Phenomena of Comets, and the apparent Reafons of them; which are from that proceeds. Seventh %