Page:Philosophical Transactions - Volume 001.djvu/177

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as to Heat or Cold: Even so nice, as that my being or not being in my Study I find to vary its hight sometimes almost a quarter of an inch.

My Baroscope, I call another Instrument for estimating the Weight or Pressure of the Incumbent Air, consisting of along Glass-tube of about 4. foot in length, and about a quarter of an inch Bore: which tube (hermetically sealed at the one end) being filled with Quicksilver (according to the Torricelian Experiment) is inverted, so as to have the open end of it immersed in Stagnant Quicksilver, contained in a larger Glass under it, exposed to the pressure of the outward Air: Out of which open end (after such immersion) the Quicksilver in the Tube being suffered to run out, as much as it will, into the Stagnant Quicksilver, in which that mouth or open end is immersed, there is wont to remain (as is commonly known to those acquainted with this Experiment) a Cylinder of Quicksilver suspended in the Tube, about 28, 29, or 30. inches high; measuring from the surface of the Stagnant Quicksilver perpendicularly; (but more or less, within such limits, according as the Weight or Pressure of the Air incumbent on the External Stagnant Quicksilver exposed to it, is greater or less:) leaving the upper part of the Tube void. (Both which Instruments being the contrivance of the Honourable Robert Boyle, they are by him more particularly described in his Physico-Mechanical Experiments touching the Air, Exper. 17. and 18. and in his Thermometrical Discourses, premised to his History of Cold.)

Now, according to both these Instruments, having kept a daily Register of Observations for more than a whole year (saving when I have been for some short time absent from home) I find my Notes for that day to be these.

January		Thermosocope	Baroscope	166$\scriptstyle {\frac {5}{6}}$
Day.	Hour	Inches.	Inches.
19.	8. Morn.	14$\scriptstyle {\frac {1}{16}}$	29$\scriptstyle {\frac {1}{2}}$	Hard frost.	Close
	4. Even.	14$\scriptstyle {\frac {3}{8}}$	29$\scriptstyle {\frac {1}{4}}$	Hard frost.	Cloudy.
	9. Even.	14$\scriptstyle {\frac {3}{4}}$	29$\scriptstyle {\frac {3}{4}}$	Rain.	Wind.
20.	8. Morn.	15$\scriptstyle {\frac {1}{4}}$	28$\scriptstyle {\frac {3}{4}}$	Sunshine.	Wind.

So that, there being in the morning (January 19.) a hard frost (which began the day before about 4. of the Clock in the after-