particularly to meafure the diameter of the planet Venus; which, according to Kepler, would amount to 7 m. according to Lanfbergius to 11 m. but which, according to his own proportion, he expected would hardly exceed one minute. He adds, that the conjunction, according to Kepler, will be Nov. 24, 1639, at 8 h. 1 m A. M. at Manchefter, the planet's latitude being 14 m. 13 f. fouth; but, according to his own correction, he expected it to happen at 5 h. 57 m. P. M. at Manchester, with 10 m. lat. fouth. But because a small alteration in Kepler's numbers would greatly alter the time of the conjunction, and the quantity of the planet's latitude, he advifes to watch the whole day, and even on the preceding afternoon, and the morning of the 25th, though he was entirely of opinion that the tranfit would happen on the 24th.

After having fully weighed and examined the feveral methods of obferving this uncommon phænomenon, he determined to tranfmit the Sun's image through a telescope into a dark chamber, rather than through a naked aperture, a method greatly commended by Kepler; for the Sun's image is not given fufficiently large and distinct by the latter, unless at a very great diftance from the aperture, which the narrownels of his fituation would not allow; nor would Venus's diameter be visible, unless the aperture were very firall: whereas, his talefcope, which rendered the folar spots diftin&tly viftble, would fhew him Venus's diameter well defined, and enable him to divide the Sun's limb more accurately.

He defcribed a circle upon paper, which nearly equalled fix inches, the narrowness of the place

VOL. IV.

not allowing a larger five; but even this fize admitted divifions fufficiently accurate. He divided the circumference into 360 degrees, and the diameter into 30 equal parts; each of which were fubdivided into 4, and the whole therefore into 190. The fubdivifion might have been carried fill farther, but he trufted rather to the accuracy and nicenefs of his

eye.

When the time of obfervation drew near, he adjufted his apparatus, and caufed the Sun's diftin&t image exactly to fill the circle on the paper; and though he could not expect the planet to enter upon the Sun's difk before three o'clock on the afternoon of the 24th, from his own corrected numbers, upon which he chiefly relied; yet because the calculations in general from other tables gave the time of the conjunction much fooner, and fome even on the 23d, he obferved the Sun on that day, but more particularly on the 24th; for on the 24th he obferved the Sun from the time of its rifing to nine o'clock; and again, a little before ten: at noon, and at one afternoon, being called in the intervals to buf nefs of the higheft moment, which he could not with decency neglect. But in all thefe times he faw nothing on the Sun's face except one fmail and common fpot, which he had feen on the preceding day, and which alfo he afterwards faw on fome of the following days.

But at 3h. 15 m. in the afternoon, which was the first opportunity he had of repeating his obfervation, the clouds were entirely difperfed, and invited hun to. feize this favourable ecurfion, which feemed to be providentially thrown in his way; for then he beheld the [Q]

moft agreeable fight, a fpot, which had been the object of his moft fanguine wishes, of an unusual fize, and of a perfectly circular fhape, just wholly entered upon the Sun's disk on the left fide, fo that the limbs of the Sun and Venus exactly coincided in the very point of contact. He was immediately fenfible that this round fpot was the planet Venus, and applied himself with the utmost care to profecute his ob

fervations.

And first, with regard to the inclination, he found, by means of a diameter of the circle fet perpendicular to the horizon, the plane of the circle being fomewhat reclined on account of the Sun's altitude, that Venus's had wholly entered upon the Sun's difk at 3h. 15m. at about 62 d. 30 m. (certainly between 60 d. and 65 d.) from the vertex towards the right hand. Thefe were the appearances with in the dark chamber.) And this inclination continued conflant at leaft to all fenfe, to the end of the obfervation.

Secondly, the following distances of the Sun's and Venus's centers were as follows:

may be expreffed as 30 to 1.12. It certainly did not amount to 1.30, nor yet to 1.20. And this was found by obferving Venus, as well when near the Sun's limb, as when farther removed from it.

The place where this obfervation was made was an obfcure village, about 15 miles diftant from Liver pool toward the north called Hool. The latitude of Liverpool had been often determined by Horrox to be 53 d. 20m. therefore that of Hool will be 53 d. 35 m. The longitude of both feemed to him to be about 22 d. 30 m. from the Fortunate Islands; that is, 14 d. 15m. to the weft of Uraniburgh.

Thefe were all the observations which the fhortness of the time allowed him to make, upon this moft remarkable and uncommon fight; all, however, that could be done in fo fmall a fpace of time he very happily executed; and scarce any thing farther remained for him to defire. In regard to the inclination alone, he could not obtain the utmoft exactnefs; for it was extremely difficult, from the Sun's rapid motion, to obferve it to any certainty within the degree: and he ingenuously confeffes that he neither did, nor could poflibly perform it. The reft are very much to be depended upon, and as exact as he could wish.

Mr. Crabtree, whom Horrox had, by letter, invited to this Uranian banquet, and who, in mathematical knowledge, was inferior to few, very readily complied with his friend's requeft, and intended to obferve the tranfit in the fame manner with Horrox; but the fky was very unfavourable to him, and was fo covered with clouds, almost during the whole day, that he gave

himfelf

himfelf upentirely to defpair. But, a little before the time of fun-fet, about 3 h. 35 m. by the clock, the Sun breaking out for the first time from the clouds, he eagerly betook himself to his obfervation, and happily faw the moft agreeable of all fights, Venus juft entered upon the Sun. He was fo ravished with this moft pleafing contemplation, that he flood for fome time viewing it leifurely, as it were; and, from an excefs of joy, could fcarcely prevail upon himself to truft his own fenfes. Upon which occafion Mr. Horrox obferves, that mathematicians have • a certain womanisn difpofition, diftractedly delighted with light and trifling circumftances, which hardly make the leaft impreffion ' upon the reft of mankind. Which levity of difpofition, let those deride that will: and with impuni" ty too. But let not any fevere Cato be ferioufly angry with thefe ' vanities of ours: for what youth, 'fuch as we are, would not fondly 'admire upon earth Venerem Soli, 'pulchritudinem divitiis conjunctam? What youth would not 'dwell with rapture upon the fair ' and beautiful face of a lady, whose charms derive an additional grace from her fortune?'.

-But, to return, the clouds deprived Mr. Crabtree of the fight of the Sun, almoft as foon as he was roufed from his reverie; fo that he was able to obferve little more than that Venus was abfolute

ly in the Sun. He could not accurately observe either the distance of Venus's center from that of the Sun, or the inclination, from the fhortnefs of the time: but as far as he could guefs by his eye, he sketch-ed out Venus's fituation upon paper, which Mr. Horrox found to agree very nearly, even to coincide with his own obfervations: nor did he err, adds his friend, more than Apelles himfelf would have done in the like hurry.He ob-ferved Venus's diameter to contain z of that of the Sun; that is, I m. 3f. according to Horrox's method of reckoning.

Thefe obfervations were made near Manchefter; the latitude of which place as determined by Crabtree is 53 d. 24 m. and its longitude is three minutes in time to the eaft of Liverpool.

Mr. Horrox acquainted his younger brother with this difcovery of Venus's tranfit, and defired him, who was then at Liverpool, to obferve it, if poffible; which he attempted, but to very little purpose, for on the 24th the fky was entirely overcaft.

Mr. Horrox, in his treatife on this fubject, publifhed by Hevelius, and from whence almoft the whole of this account has been collected, hopes for pardon from the aftronomical world, for not making his intelligence more public; but his difcovery was made too late. He is defirous, however, in the fpirit

OF

of a true philofopher, that other aftronomers were happy enough to obferve it, who might either confirm or correct his obfervations. But fuch confidence was repofed in the tables at that time, that it does not appear that a tranfit of Venus was ever obferved but by our two ingenious countrymen, who profecuted their aftronomical studies with fuch eagerness and precifion, that they must very foon have brought their favourite science to a degree of perfection unknown to thofe times. But unfortunately Mr. Horrox died on the 3d of January 1640-1, about the age of 25, juft after he had put the laft hand to his treatife, intituled, Venus in Sole visa, in which he fhews himself to have had a

more accurate knowledge of the dimenfions of the solar system than his learned commentator Hevelius.

Mr. Crabtree died on the 1ft of Auguft 1644, at Manchester, as appears, if I am rightly informed, by the regifter of that place. Cotemporary with these two illuftrious youths lived William Gafcoigne, the inventor of the Micrometer, who was flain at Marfton-moor on the 2d of July 1644, fighting for king Charles I. at the age of 23. The exact age of Mr. Horrox is not known; but, perhaps, fome of your Cambridge correfpondents may be able to inform us by confulting the univerfity books, as Mr. Horrox was educated at Emanuel college.

Yours, ASTROPHILUS.