<p style='text-align: justify;'>Isaac b. Solomon ibn al-Aḥdab b. Ṣaddiq Sefardi's <i>The Epistle of the Number</i> was composed at the end of the 14th century after Isaac settled in Syracuse, Sicily, and this is the only known copy of the work. The Epistle is a translation and enlargement of the famous <i>Talḵīṣ ʿAmal al-Ḥisāb</i> ('A summary of the operations of calculation', 13th century) by the Moroccan Muslim mathematician Ibn al-Bannā ابن البنّاء and it is especially notable in being the first known treatise in Hebrew to include extensive algebraic theories and operations. The Epistle attests novel mathematical vocabulary and enhances our linguistic understanding of the mechanisms that helped create the scientific vocabulary of Medieval Hebrew. The work proper begins on f.<a href='' onclick='store.loadPage(2);return false;'>1v</a>, with an explanation of how Isaac came to compose the Epistle. Book 1, arithmetical operations on integers, fractions and roots is on ff.<a href='' onclick='store.loadPage(2);return false;'>1v–25r</a>, and consists of three parts: part 1, arithmetical operations on integers; part 2, arithmetical operations on fractions; and part 3, arithmetical operations on the roots of expressible (rational) and inexpressible (irrational) quantities. Book 2, the rules which enable us to obtain the unknown from the given known, is on ff.<a href='' onclick='store.loadPage(53);return false;'>27r–38v</a>, and also consists of three parts: part 1, proportions and scales; part 2, the algebraic operations of restoration and operation; part 3, solution of problems of a practical nature by methods of algebra. The last words in part 3, on folio 38v, are 'another example', thus the manuscript is truncated. First words and headings are written in larger, bolder script; some words and the numerals in calculations are rubricated. There are tables with both Hebrew and Arabic numerals, as well as diagrams. There are occasional marginal calculations in a different hand, e.g., f.<a href='' onclick='store.loadPage(11);return false;'>6r</a>, as well as manicules, e.g., f.<a href='' onclick='store.loadPage(14);return false;'>7v</a>. Diagrams include the place-value numerical system with zero and Hindu-Arabic numerals, f.<a href='' onclick='store.loadPage(3);return false;'>2r</a>; various scales, ff.<a href='' onclick='store.loadPage(50);return false;'>25v–26v</a>; and multiplication tables of algebraic expressions, f.<a href='' onclick='store.loadPage(68);return false;'>34v</a>. Unrelated to the Epistle, f. <a href='' onclick='store.loadPage(1);return false;'>1r</a> describes a mathematical problem, with a diagram of two birds sitting on two towers of unequal height, and referring to Elijah Mizraḥi אליה המזרחי in the last line. Various elaborate signatures and owners' marks follow in the lower half of the leaf, including the name Judah Eli יאודה עלי.</p>
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