of _June_, in the year 1761; till which time we must content ourselves with allowing the Sun’s distance to be about 81 millions of miles, as commonly stated by Astronomers. [Sidenote: The Sun proved to be much bigger than the Moon.] 192. The Sun and Moon appear much about the same bulk: And every one who understands Geometry knows how their true bulks may be deduced from the apparent, when their real distances are known. Spheres are to one another as the Cubes of their Diameters; whence, if the Sun be 81 millions of miles from the Earth, to appear as big as the Moon, whose distance does not exceed 240 thousand miles, he must, in solid bulk, be 42 millions 875 thousand times as big as the Moon. 193. The horizontal Parallaxes are best observed at the Equator; 1. Because the heat is so nearly equal every day, that the Refractions are almost constantly the same. 2. Because the parallactic Angle is greater there as at _A_ (the distance from thence to the Earth’s Axis being greater,) than upon any parallel of Latitude, as _a_ or _b_. [Sidenote: The relative distances of the Planets from the Sun are known to great precision, though their real distances are not well known.] 194. The Earth’s distance from the Sun being determined, the distances of all the other Planets from him are easily found by the following analogy, their periods round him being ascertained by observation. As the square of the Earth’s period round the Sun is to the cube of it’s distance from him, so is the square of the period of any other Planet to the cube of it’s distance, in such parts or measures as the Earth’s distance was taken; see § 111. This proportion gives us the relative mean distances of the Planets from the Sun to the greatest degree of exactness; and they are as follows, having been deduced from their periodical times, according to the law just mentioned, which was discovered by KEPLER and demonstrated by Sir ISAAC NEWTON. _Periodical Revolution to the same fixed Star in days and decimal parts of a day._ Of Mercury Venus The Earth Mars Jupiter Saturn 87.9692 224.6176 365.2564 686.9785 4332.514 10759.275 _Relative mean distances from the Sun._ 38710 72333 100000 152369 520096 954006 _From these numbers we deduce, that if the Sun’s horizontal Parallax be 10ʺ, the real mean distances of the Planets from the Sun in English miles are_ 31,742,200 59,313,060 82,000,000 124,942,580 426,478,720 782,284,920 _But if the Sun’s Parallax be 11ʺ their distances are no more than_ 29,032,500 54,238,570 75,000,000 114,276,750 390,034,500 715,504,500 Errors in distance a rising from the mistake of 1ʺ in the Sun’s Parallax 2,709,700 5,074,490 7,000,000 10,665,830 36,444,220 66,780,420