THE TRANSIT OF VENUS.

Evening Star, Issue 3710, 13 January 1875, Page 3

THE TRANSIT OF VENUS.

. To the Editor. Sir, —My reply to the question of your correspondent “Inquirer” must be partly mathematical, and wholly dry, I can only hope that my remarks will “oblige many of your readers,” as “ Inquirer ” says they will, but I am somewhat inclined to doubt it.

Gosse, in his “ Evenings with the Micro scope,” says that the average breadth of the human hair is of an inch. Dividing this by 12, we find that the breadth of a human hair is —of afoot. 3995

Again, multiplying the 360 degrees in a circle by 60, and the product also by 60, we find that there are 1,293,000 seconds in a circle ; dividing this by 8.9 (the'un’s equa torial horizontal parallax), we find that in a circumference of a circle the qqiQunt qf this parallax ig contained 145,618 times nearly. Evidently then 1 . . 1 145615t * * 3996 * w^°^e circumference

of circle in feet, which gives the answ'er 36.45 ft nearly. Dividing this by 3.14159 (the ratio of circumference to diameter) wc obtain 11.0 ft nearly for the diameter ; and this again by 2 we get 5.8 feet for the radius, or the distance at which a hair mu-t be placed so as to subtend an angle of 8 9 seconds. If we wish now to find what must be the distance of a hair so that it may subtend an 3 , angle of of a second we haye plainly only to divide 8.9 by which gives us tbg

answer 29.6 ; now multip'ying 5.8 feet by 29.6 we get for our answer 172.06 feet nearly. It is extremely improbable that Professor Peters made the statement contained in the report referred to. If he did make such a mistake, it must have been through a mere oversight. The problem may be easily solved, as above, by means of arithmetic and a little, a very little, mensuration, and it can present no more difficulty to Professor Peters than would a sum in sixmde addition to a good arithmetician. “Inquirer” will find the passage he asks information about in Herschel’s “Outlines of Astronomy.” somewhere near the beginning of the book, I believe. It will, of course, be seen that one three hundred andthirty-third, of an inch has been taken as the length of the arc subtending the angle 8 9 sees , and not a 3 representing the sine of that angle (wh-ch might have b en dpne in tfie ca*e of so minute au angle), or the chord of the arc,—l am. Hough Astronomical Notes, P.S.—lf such a problem requires proof, here it is;— A" s? 206265 7 x a r A 3995 WM 172.06 A = 2t)(j265 3996 687573 A = 20626S ~ of a secon d, very nearly.