(Extracts from his work)
"The chance of a clouded atmosphere caused me much anxiety; for Jupiter and Mercury were in conjunction with the Sun almost at the same time as Venus.
This remarkable assemblage of the planets (as if they were desirous of beholding, in common with ourselves, the wonders of the heavens, and of adding to the splendour of the scene), seemed to forebode great severity of weather.
Mercury, whose conjunction with the Sun is invariably attended with storm and tempest, was especially to be feared. In this apprehension I coincide with the opinion of the astrologers, because it is confirmed by experience; but in other respects I cannot help despising their more puerile vanities...
Having attentively examined Venus with my instrument, I described on a sheet of paper a circle whose diameter was nearly equal to six inches, the narrowness of the apartment not permitting me conveniently to use a larger size.
This however admitted of a sufficiently accurate division; nor could the arc of a quadrant be apportioned more exactly, even with a radius of fifty feet, which is as great a one as any astronomer has divided; and it is in my opinion far more convenient than a larger, for although it represents the Sun's image less, yet it depicts if more clearly and steadily. ...
When the time of the observation approached, I retired to my apartment, and having closed the windows against the light, I directed my telescope, previously adjusted to a focus, through the aperture towards the Sun and received his rays at right angles upon the paper already mentioned.
The Sun's image exactly filled the circle, and I watched carefully and unceasingly for any dark body that might enter upon the disk of light. I then beheld a most agreeable spectacle, the object of my sanguine wishes, a spot of unusual magnitude and of a perfectly circular shape, which had already fully entered upon the Sun's disk on the left, so that the limbs of the Sun and Venus were precisely coincided, forming an angle of contact.
Not doubting that this was really the shadow of the planet, I immediately applied myself sedulously to observe it. In the first place, with respect to the inclination, the line of the diameter of the circle being perpendicular to the horizon, although its place was somewhat inclined on account of the Sun's altitude, I found that the shadow of Venus at the aforesaid hour, namely fifteen minutes past three, had entered the Sun's disk about 62° 30', certainly between 60° and 65°, from the top towards the right.
This was the appearance in the dark apartment; therefore out of doors beneath the open sky, according to the laws of optics, the contrary would be the case, and Venus would be below the centre of the Sun, distant 62° 30' from the lower limb, or the nadir, as the Arabians term it. The inclination remained to all appearance the same until sunset, when the observation was concluded.
In the second place, the distance between the centres of Venus and the Sun I found, by three observations, to be as follows:
At 3.15 by the clock 14'24"
At 3.35 by the clock 13'30"
At 3.45 by the clock 13'0"
At 3.50 the apparent sunset.
The true setting being 3.45, and the apparent about five minutes later, the difference being caused by refraction. The clock therefore was sufficiently correct. In the third place, I found after careful and repeated observation, that the diameter of Venus, as her shadow was depicted on the paper, was larger indeed than the thirtieth part of the solar diameter, though not more so than the sixth, or at the utmost the fifth, of such a part.
Therefore, let the diameter of the Sun be to the diameter of Venus as 30' to 1'12". Certainly her diameter never equalled 1'30", scarcely perhaps 1'20", and this was evident as well when the planet was near the Sun's limb, as when far distant from it. This observation was made in an obscure village where I have long been in the habit of observing, about fifteen miles to the north of Liverpool, the latitude of which I believe to be 53° 20'; although by the common maps it is stated at 54° 12'
This is all I could observe respecting this celebrated conjunction, during the short time the Sun remained in the horizon; for although Venus continued on the disk for several hours, she was not visible to me longer than half-an-hour, on account of his so quickly setting.
Nevertheless, all the observations which could possibly be made in so short a time, I was enabled, by Divine Providence, to complete so effectually that I could scarcely have wished for a more extended period.
The inclination was the only point upon which I failed to attain the utmost precision; for, owing to the rapid motion of the Sun, it was difficult to observe with certainty to a single degree, and I frankly confess, that I neither did not nor could ascertain it. But all the rest is sufficiently accurate, and as exact as I could desire."
See his published diagram showing his observations of transit of Venus across the sun
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