II. A letter of Mr. W. Derham, Rector of Upminster, dated Jan. 13. 1697/98. to Dr. Sloane, about a contrivance to measure the height of the mercury in the barometer, by a circle on one of the weather plates, with a register of weather, &c. for the year 1697.

Abstract

To my former Observations about the Barometer, give me leave to subjoin a Contrivance for measuring the Height of the <italic>Mercury</italic>, which hath lately occurred to my Thoughts, and which in some Cases is more commodious, than that way with a crooked Tube (I spake of) This way is by a Circle on one of the Weather-plates, of any convenient Diameter.