Page:Philosophical Transactions - Volume 001.djvu/168

 drawn up so Invisibly, that the Air and Sky seem'd very clear all day long. This I account a great change between ascending and descending Dews and Vapors (which import Levity and Weight,) and between thick Air and clear Air; which changes do sometimes continue in the Alternative course of day and night, for a week or fortnight together, and yet the Baroscope holding the same.

13. Sometimes (I say not often) the Baroscope yields not to other very great changes of the Air. As lately (December 18.) an extraordinary bright and clear day; and the next following quite darkned, some Rain and Snow falling; but the Mercury the same: so in high winds and calms the same.

14. I do conceive, that such as converse much Sub dio, and walk much abroad, may find many, particulars much more exactly, then I, who have no leisure for it, can undertake. To instance in one of many, December. 16. last, was a clear cold day, very sharp and strong East wind, the Mercury very near 30. inches high, about three in the afternoon, I saw a large black cloud, drawing near us from the East and South-East, with the East-wind. The Mercury changed not that day nor the day following; the Stars and most of the sky were very bright and clear till Nine of the Clock; and then suddenly all the sky was darkned, yet no change of weather happened; December 17. the frost held, and 'twas a clear day, till about two of the clock in the afternoon; and then many thick clouds appear'd low in the West, yet no change of the weather here; the Wind, Frost, and Quick-siver, the same, December 18. the Mercury fell almost of an inch, and the sky and Air so clear and bright and cold with an East-wind, that I wondred what could cause the Mercury to descend. I Expected, it should have ascended, as usually it does in such clear skys. Casually I sent my servant abroad, and he discovered the remote Hills, about 20. miles off, cover'd with Rh