The Sun as the centre of the system will first occupy our attention. The distance of the Earth from the Sun, which is usually employed by astronomers as a unit of measurement, has been ascertained with great accuracy, from the transit of Venus over the disc of the latter in 1769, to be 95,298,260 miles, a distance which every successive transit will render more and more exactly known. Having ascertained the true mean distance of the Earth from the Sun, it is not difficult to determine, by trigonometry, the true diameter of the latter body, its apparent diameter being known from observation; and as the most reliable results prove that the Sun, in the above position, subtends an angle of about 32', it follows that its true diameter is about 887,000 miles; the volume of this enormous globe, therefore, exceeds that of the Earth 1,400,000 times; in other words, it would take 1,400,000 Earths to make up a globe of the same size as the Sun. The Sun's mass, or attractive power, exceeds that of the Earth 355,000 times, and is 476 times greater than the masses of all the planets put together.