The INTRODUCTION:

Periods, perform their Revolutions fromWest to East, in the following Order.

i. J Mercury is nearest to the Sun of all jthe Planets, and performs its Course inabout three Months. 2. 2 Venus in aboutseven Months and a half. 3. ® The Earth [in a Year. 4. cs Mars in about two Years.

5. 1L Jupiter in twelve. And, lastly, h Sa-turn, whose * * Orbit includes all the rest, |spends almost 30 Years in one Revolution jround the Sun. The Distances of the Pla-nets from the Sun are nearly in the lameProportion, as they are represented in Elate |jj1 . viz. Supposing the Distance of theEarth from the Sun to be divided into 10equal Parts; that of Mercury will be about4 of these Parts; of Venus 7 ; of Mars 15 ;of Jupiter 52; and that of Saturn 95.

The Orbits of the Planets are not allin the fame Plane, but variously inclinedto one another; so that supposing one ofthem to coincide with the above Scheme,the others will have one half above, andthe other half below it; intersecting one Janother in a Line passing through the Sun.The Plane of the Earth’s Orbit is called

the

Note, The Characters placed before the Names of the Planetsare for Brevity-Iake commonly made use of by Astronomers,instead of the Words at length, as { tor Venus, < 're.

* By the Orbit of a Planet, is commonly understood theTract or Ring described by its Center round the Sun; but bythe Plane of the Orbit is meant a flat Surface extended everyway through the Orbit infinitely.