And now for a clofe, I fhall take this opportunity of publicly owning, with all honour and thankfulness, the generous offer made me by fome of my friends, eminent in their stations, as well as skill and abilities in the laws, who would have made me a prefent of the May-pole in the Strand (which was to be taken down) or any other pole. I thought convenient for the management of Mr. Huygens's glafs. But as my incapacity of accepting the favour of thofe noble Mecœnates, hath been the occafion of that excellent glass being put into better hands; fo, I affure myself, their expectations are abundantly answered, by the number and goodness of the observations that have been, and will be made therewith.

A PRE

A PRELIMINARY

DISCOURSE,

CONCERNING

THE SYSTEMS OF THE HEAVENS, THE HABITABILITY OF THE PLANETS, AND A PLURALITY OF WORLDS, USEFUL FOR THE READING OF THE FOLLOWING BOOK,

MY Phyfico-Theology having met with fo

quick a fale as to come to a third impreffion before the year was expired, but efpecially the folicitations of many learned men, both known and unknown, have given me great encouragement to fulfil my pro nife, in fending abroad this other part, relating to the heavens: which fhould fooner have feen the light, but that I was minded not to interrupt the reader's patience with many notes (which I could not well avoid in my Phyfico-Theology, and which my rough draught of this was burthened with) and therefore I threw the greatest part of them into the text: which neceffitated me to tranfcribe the whole. And when my hand was in, I new. made fome part of it, and added many new obfervations of my own, which I have lately made with fome very good long glaffes, I have in my Vol. II. M hands;

hands; one of Campani's grinding; and others of English work, which exceed it; but especially one of Mr. Huygens's of about 126 feet, which few for goodness do furpass.

Of thefe obfervations the reader fhould have met with many more (and I believe fome of my ingenious friends do expect more) but that I lay under two inconveniences. One the want of an open free horizon, my habitation being furrounded much with trees. The other, and indeed the chief, the want of a long pole of 100 or more feet, to raise my long glafs to fuch an height as to see the heavenly bodies above the thick vawhich much obfcure all objects near the pours; horizon, especially when viewed with long and good glaffes. But as I have been at confidérable expences already about these matters, and this I am informed would amount to 80 or gol. I thought it too great a burthen for me to bear.

And, therefore, if I have not fufficiently anfwered the expectations of fome of my learned and ingenious friends, I hope they will excufe me, and I believe it to be more my calamity than fault that I have done no more: especially among fuch planets as have advantageously pres fented themselves, as Saturn particularly hath, whose five or more fatellites it may be expected

I have feen; but I could never reach but three of them, and they only, when there were but few vapours. And as for the fpots in Mars and Venus, and their motion round their own axis, I confefs I have not yet had good views of those planets, fince I have had my furniture of glaffes, by reafon of the too great diftance of Mars from the earth, and the proximity of Venus to the Sun, and of late the cloudy weather, and the fmall altitude which Venus hath above the horizon. But if I can obtain a fufficient apparatus, and God is pleased to grant me life, health, and leifure, I hope to compenfate for my defects.

But, however, what is here wanting in my own, is fufficiently made up from the obfervations of others, of which the learned world hath good ftore, fince the invention of the telescope; which as it hath made ample difcoveries of the works of God, fo hath laid open a new, and a far more grand and noble scene of those works, than the world before dreamt of, and afforded us a far more rational system of the heavens and the univerfe, than was before entertained.

And forafinuch as I have frequent occafions in my following book to speak of, and according to this and fome of the other fyftems, it is neceffary I should by way of preface, give some account of them to enable fuch perfons to read my book as are unacquainted with aftronomical matters.

Among all the various fyftems, I need take notice only of three, the Ptolemaic, the Copernican and the new fyftem. Of each of which in their order.

OF THE PTOLEMAIC SYSTEM.

In the Ptolemaic fyftem the earth and waters are fuppofed to be in the centre of the univerfe; next to which is the element of air, and next above that is the element of fire; next that, the orb of Mercury, then that of Venus, then that of the Sun; and above the Sun's orb, thofe of Mars, Jupiter, and Saturn; and above them all the firmament, or orb of the fixt ftars; then the cryftalline orbs; and laftly the cælum empyreum, or heaven of heavens. All these maffy orbs, and vaft bodies borne by them, are in this fyftem, fuppofed to move round the terraqueous globe once in 24 hours; and befides that, in fome other certain periodical times. For the effecting of which motions, they were forced to contrive fuch circles as they called eccentrics and epicycles, crof fing and interfering with one another; which I could not reprefent in fo narrow a compafs as Fig. 1. is, that is a scheme of this Ptolemaic fyftem; which is univerfally maintained by the Peripatetic philofophers.

OF