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so that they differ among themselves more thanfrom the true observations, which makes it impos-sible to reconcile such incontinences; however,tis sufficient to thew that this Comet kept a tractvery similar to that of 1682, and if you make alittle addition to the latitude, almost the very fame.

As this Theory agrees With the real observations ofthree different Comets, made in 153 1 „i 607, and 1687,it would be next to a miracle it th, ee different Co-mets should three times keep the fame tract, andmore than a miracle if it were not the third revo-lution of the fame Comet, in an elliptic curve :It therefore he lays it appears again about the year1758, impartial posterity must needs allow this tobe the discovery of an Englijhman.

And this he fays is as it were the Mercury ofComets revolving round the Sun in the smallestOrbit, whilst others appear not again under thespace of a hundred, and some of many hundredyears ; at which time, arriving in the neighbour-hood of the Sun, they thine with a greater lustre,and fend forth conspicuous tails, which are no-thing but subtle vapors exhaled from the body ofthe Comet by the intenfenefs of the Sun’s heat, assteam from water set over the fire; but concern-ing this he refers to Newton according to his cus-tom, arguing very forcibly at the end of the thirdbook of his Principia , who therein, among otherthings, enters into the following speculation; towit, that the earth (by furnishing such a quantityof moisture for the growth of vegetables, whichwhen they wither become dry substances) wouldin a sufficient length of time be exhausted, and lesta hard and dry body, unless supply’d by somemeans or other: Now the tails of Comets, like

other