SPLENDID PROTRACTOR BY THOMAS HEATH
Stock Number: 7264
SPLENDID PROTRACTOR WITH FIVE - ARCMINUTE TRANSVERSAL WINDOW SYSTEM, signed "T:Heath Fecit."
8 inch diameter (20 cm)
Country of manufacture
UK and Ireland
SPLENDID PROTRACTOR BY THOMAS HEATH WITH FIVE – ARCMINUTE TRANSVERSAL WINDOW, English, c.1725, signed “T:Heath Fecit.” The 8″ diameter (20 cm) semicircular brass protractor is hand-divided every degree, with beautiful bold numbering every 10° from 0° to 180° (and from 180° to 360°). The left side is pierced with a window and transversal running from 0° to 1°, itself divided every five arcminutes from 0 to 60. It is further pierced with a central rectangle, and decorated with bold elegant hand engraved “leaves” in the corners. Scales of polygon angles (from 4-sided to 12-sided) are laid out against the degree scales (from 90° down to 30° and up to 150°), and the base of the protractor is finely divided with a scale of four parts per inch, each part subdivided to tenths. Condition is generally fine throughout, noting minor signs of use.
Heath was an exceptional maker, but instruments by him appear infrequently on the market. This one is remarkable in its use of a transversal window, a feature we have seen rarely, once by Edmund Culpeper, and again by Heath (see Millburn’s article SIS Bulletin 50, pp. 25-26). In use one measures an angle by placing the protractor’s centerpoint on the angle’s vertex, placing the crossbar more or less along the baseline (the first side of the angle) rotating the protractor slightly (less than 1°) until the second side exactly cuts an integral number of degrees (or half degrees), and reads the additional minutes where the transversal cuts the baseline. It is a practical, fast technique for reading (or marking) headings, etc. to five arcminutes or better.
David and Yola Coffeen both have enjoyed academic careers, as planetary astronomer and as linguist/educator. But since 1982 (yes, 1982!) they have been full-time dealers in early scientific and medical instruments, under the name Tesseract. Selling primarily by catalogue (over 100 issued so far) they also have a web presence at www.etesseract.com, and can be contacted at [email protected]
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