LET. XVIII. OF THE SUN, MOON, AND PLANETS. 3O7

surface, and from its center, is greater or less,according as the fun is nearer to or further fromthe earth, it \^ill be easy to find what this dif-ference must be at all kinds of distances of thefun from the earth. The observer, therefore,by knowing how much shorter the duration ofthe transit appears to him upon the earth’s sur-face, than it would have done if he had been atrest at the center, may readily find the distanceof the sun from the earth, which was the thingto be determined.

The transits which happened in the years 1761and 1769, were observed with the greatest accu-racy and diligence by some of the most eminentAstronomers in Europe, who were sent out tothe most convenient parts of the earth for thatpurpose; and from their determinations it ap-pears, that the horizontal parallax of the fun is,at a mean, about eight and a half seconds, andhis distance from the earth, in round numbers,about ninety-five millions of miles. A distanceso prodigious, that a cannon-ball, which is knownto move at the rate of about eight miles in aminute, would be something more than twenty-two years in going from the earth to the sun^and if a spectator could be placed in the sun,and was to look at the semi-diameter of theearth, this line, which is about four thousandmiles long, would only appear to him under anan gle of about eight and a half seconds. Con-fa' X 2 sider