Jefferson, Thomas (1743-1826) [Description of a rain-gauge]
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Gilder Lehrman Collection #: GLC06572 Author/Creator: Jefferson, Thomas (1743-1826) Place Written: s.l. Type: Autograph note Date: circa 1815 Pagination: 1 p. ; 11.2 x 10.5 cm Order a Copy
A scientific note on the design of a rain gauge. Includes 18 lines on the measurement (volume and weight) of rain, written on the verso of a fragmentary address leaf to John Gads[incomplete]. "The area of the funnel is 10. square inches. The fall of an inch of rain then delivers 10. cubic inches into the funnel." He notes the weight of a cubic inch which was used to mark, successively, each point on the gage and concludes that this system "renders unnecessary all attention to the ratio of the area of the funnel and measuring tube, or to the inequalities of the caliber of the measuring tube." Jefferson refers to James Joyce's Scientific Dialogues, which was issued in 2-3 volumes in 1815, 1817 and 1819, when he writes at the bottom of the page, "see 2. Scientific dialogues. conversn. 48 [or 4b]." Not dated, circa date inferred from publishing date of Joyce's Dialogues.
See GLC6572.02 for Joyce's Dialogues.
Rain-gage
The area of the funnel is 10. square inches. The fall of an inch of rain then delivers 10.cubic inches into the funnel.
A cubic inch of rain water weighs 253.16 grains Troy
253.16 grs. of rain water were accurately weighed, poured into the measuring tube if a glass and marked on it as the measure of 1/10 I. fall of rain on an area of 10. sq. inches
then double that weight was poured in & marked as 2/10
the[n] treble was weighed[,] poured in & marked as 3/10 ____ according to the height of the tube.
Each of these spaces, denoting 1/10 was then subdivided by compasses, marked and denoted 1.cent of an inch fall of rain.
This renders unnecessary all attention to the ratio of the area of the funnel and measuring tube, or to the inequalities of the caliber of the measuring tube.
see 2. Scientific dialogues. Convers[atio]n. 48 [or 4b]
[Address leaf, verso:]
John Gads<den?>
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