Fig. V. is that of the great _Alphonsus_, _Fernelius_, _Regiomontanus_, _Amicus_, _Maurolycus_ and _Langius_; also of _Azabel_, _Thebit_, and _Isaac Israelita_; and likewise of _Gulielmus Parisiensis_, and _Johannes Antonius Delphinus_. Consisting of Ten Heavens, made up of A _Primum Mobile_ S _Empyræum_. A Sphere of _Tripidation_ in Longitude R _Primum Mobile_. The Sphere of the fixed Stars A And those of the seven solar Planets within. _Note_, Some Authors place the Sphere of _Tripidation_ in Longitude below that of the _Aplain_, or Eighth Sphere. Lastly, Fig. VI. is the Heaven of _Petrus Alliacensis_, the College of _Conimbra_, _Martinensis_, (and sometime) of _Clavius_; and also _Johannes Warnerus_, _Leopoldus de Austriâ_, _Johannes Antonius Maginus_; and lastly, of _Clavius_. In all Eleven Heavens containing, T A _Primum Mobile_, or, as others say, an _Empyræum_. V A Sphere of Libration in Latitude. W A Sphere of Libration in Longitude. A The Sphere of the fixed Stars, and those of the Planets. [Illustration: Plate III. The Seven Planetary orbits. ] Thus you see how many various Opinions have from time to time been embraced concerning the Fabric and Formation of the visible Universe; all of which are now and have long been exploded; and although at first advanced by Men of the greatest Learning, and of the deepest Penetration in natural Knowledge, it does not appear from any one of their Opinions, that they had any the least Notion of infinite Space, but as it were confined the Divine Being to their limited Notions, as one may say in an Egg-shell. If therefore what I shall hereafter advance, extend so far without the known Creation, that you can possibly conceive no Bounds to the Works of infinite Wisdom and Power, I hope you will be in no Danger of looking upon it as more ridiculous, or absurd, than what so many of the wisest Men of every Age have thought proper to attempt, and have judged worthy of their Attention so long before me. If any thing less so, I shall think myself happy enough in having broke, or rather passed the narrow Limits to which the Creation has for so many Years been confined, in hopes of tempting Men of greater Talents to look up wards, and pursue so noble a Subject as far as the human Understanding is capable of comprehending it. To the Opinions above might be added many more, particularly that of _Johannes Baptista Turrianus_, and _Fracastorius_, who increased the Number of Heavens to fourteen, _viz._ seven on each Side the _Aplané_. But of this I have said enough; in my next I shall proceed to Matter better grounded, _And am_, &c. [Illustration] LETTER the THIRD. _Concerning the Nature, Magnitude, and Motion of the Planetary Bodies round the Sun_, &c. _SIR_,