Philosophical Transactions. For the months of Jan. Febr. and March 1716. - Part IV.

Ⅳ. Some late curious astronomical observations communicated by the Reverend and Learned Mr. James Pound, Rector of Wansted, and R. Soc. Soc.

The occultation of Jupiter by the moon observed at Wansted the 14th of July in the morning, 1715.

Having after midnight carefully corrected the clock by no less than ten observations of the altitude of the Lucida Arietis, the error thereof was found 5'.13". too fast, the extreams not differing above 6"; and in the morning about 7h, by as many altitudes of the sun. With a like agreement, the same error was found 5'. 14", to be deducted from the times shewn by the clock.


Jupiter and the satellites were to the Northward of the visible way of the moon's center.
This occultation was observed through a telescope, in which the focal length of the object glass was 14 ½ feet, and of the eye glass 2 ¾ inches. And the aperture of the object glass was Ⅰ 1/10 inch.
I could perceive no colours on Jupiter's limb, either at his immersion or emersion, when the axis of the tube was directed to him.


At 17h. 39'. the eclipse was thought to be ended; and was visibly so at 17h. 41'; but by comparing the last observations of the chords between the horns, it follows that the true end of the eclipse was at 17h. 38'. 20". At 17h. 43 the moon's diameter was 33'. 40".
The middle cannot be supposed to be very accurately determined by these observations, which were not sufficiently distant from the time of the greatest obscuration. However by comparing several of them together, the middle will be obtained, viz.


By reason of clouds I could not see the beginning of the eclipse, nor make such observations of the moon's immerging into the shadow as I did of her emerging out of it.
By observation Ⅱ. compared with observation 15 the digits eclipsed were 8 ¾.
The angles were measured by a micrometer in a 15 foot telescope. I have not considered how far they are consistent with one another; they being set down here exactly as they were first taken.
This eclipse is the more considerable, as happening very near the moon's perigee, and therefore useful to verify her anomaly; as also to limit the greatest diameter of the shadow of the earth, and consequently the parallax of the moon. This may very properly be compared with that of the 19th of October, 1697, whose middle was at 7h. 41'. P.M. at London, and the quantity the same as now.
The times by the clock were 17'..45". sooner than the apparent time, as was found by the following observations of Cor Leonis and Arcturus, which through the clouds were but just discernible.

The latitude of Wansted is 51°. 34' Its longitude is 8" in the time Eastward from the observatory at Greenwich.
The account given of this eclipse by the Reverend Mr. William Derham, who observ'd it at Upminster, is agreeable to this, as far as clouds would permit him to observe.

A pdf version of the entire text of the Philosophical Transactions of the Royal Society of London can be found here (this article begins on page 401).

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