An Account of the Sun's Distance from the Earth, Deduced from Mr. Short's Observations Relating to the Horizontal Parallax of the Sun: In a Letter from Peter Daval, Esq; V. P. of R. S. to James Barrow, Esq; V. P. of R. S.

I. An Account of the Sun's Distance from the Earth, deduced from Mr. Short's Observations relating to the horizontal Parallax of the Sun: In a Letter from Peter Daval, Esq; V.P. of R.S. to James Barrow, Esq; V.P. of R.S. Read Jan. 13, 1763. According to Mr. Short, the mean horizontal parallax of the Sun is $8''$, $65$. Now this parallax is the angle, which the semidiameter of the earth subtends, being seen from the Sun. Therefore as $8''$, $65$, is to $360^\circ$ (the whole periphery of a circle) so is the semidiameter of the earth to the periphery of the orbit of the earth round the Sun. Sun. But $8''$, $65$, is very nearly $\frac{1}{360}$th part of $360^\circ$, as may be easily proved by division. According to the latest observations, the mean semidiameter of the earth is $3958$ English miles, which being multiplied by $149,826$ produces $593,011,308$ miles for the circumference of the orbit of the earth. The distance of the earth from the Sun is the semidiameter of this orbit: and the periphery of the circle is to its semidiameter very nearly as $6,283,185$ to one. Therefore if we divide $593,011,308$ by $6,283,185$ the quotient, which is very nearly $94,380,685$, will give the mean distance of the earth from the Sun in English miles. N. B. As the orbit of the earth is an ellipse, not a circle, the distance of the earth from the Sun will be greater in its aphelion, and less in its perihelion, than here assigned. Dear Sir, I have from Mr. Short's observations deduced, as above, the mean distance of the Sun from the earth, and am pretty sure I have made no material mistake. I am Your's entirely, Dec. 18, 1762. Peter Daval.