(156)
The Exclusion of all Air is here necessary, because Air being subject to the operation of Heat and Cold, if any of it remain in the Barometer, it will cause it to vary from shewing the true Pressure of the Air. to a Mercurial Cane, and take all my Notes from it, This Cane is but 35. Inches long, of a very slender Cavity, and thick Glass. This may easily be conveyed to any place, for Trials. The Vessel for the stagnating Mercury, into which the said Cane is immersed, is about two Inches wide. The Mercury so well fill'd, that for some daies it would not subside, but hung to the top of the Glass cane. I keep it in a Closet pretty close, 9. foot high, 8. foot broad, 15. foot long; neer a Window. This I note, because possibly the closeness of the room may hinder, that it gives not the full of all Changes, as it might in a more passable Air.
2.In all my Observations from May 28. 1664 to this present (December 9. 1665.) the Quicksilver never ascended but very little above 3014 Inches.
3. It ascended very seldom so high (videl. to 3014 Inches) chiefly in Decemb. 13. 1664. the weather being fickle-fair, Evening.
4. I find by my Calender of June 22. 1664. at 5. in the Morning, in a time of long setled fair weather, that the Mercury had ascended about half an Inch higher then 30: but I fear some mistake, because I then took no impression of wonder at it; yet for 3. or 4. daies, at that time it continued high, in well-setled, fair and warm weather; most part above 30. Inches. So that I may note, the Mercury to rise as high in the hottest Summer, as in the coldest Winter-weather.
5. Yet surely I have noted it ascend a little higher for the Coldness of the Weather; and very frequently, both in Win-
