Mathematical astronomy

The sexagesimal method developed by the Babylonians has a far greater computational potential than what was actually needed for the older problem texts. With the development of mathematical astronomy in the Seleucid period, however, it became indispensable. Astronomers sought to predict future occurrences of important phenomena, such as lunar eclipses and critical points in planetary cycles (conjunctions, oppositions, stationary points, and first and last visibility). They devised a technique for computing these positions (expressed in terms of degrees of latitude and longitude, measured relative to the path of the Sun’s apparent annual motion) by successively adding appropriate terms in arithmetic progression. The results were then organized into a table listing positions as far ahead as the scribe chose. (Although the method is purely arithmetic, one can interpret it graphically: the tabulated values form a linear “zigzag” approximation to what is actually a sinusoidal variation.) While observations extending over centuries are required for finding the necessary parameters (e.g., periods, angular range between maximum and minimum values, and the like), only the computational apparatus at their disposal made the astronomers’ forecasting effort possible.

Within a relatively short time (perhaps a century or less), the elements of this system came into the hands of the Greeks. Although Hipparchus (2nd century bce) favoured the geometric approach of his Greek predecessors, he took over parameters from the Mesopotamians and adopted their sexagesimal style of computation. Through the Greeks it passed to Arab scientists during the Middle Ages and thence to Europe, where it remained prominent in mathematical astronomy during the Renaissance and the early modern period. To this day it persists in the use of minutes and seconds to measure time and angles.

Aspects of the Old Babylonian mathematics may have come to the Greeks even earlier, perhaps in the 5th century bce, the formative period of Greek geometry. There are a number of parallels that scholars have noted. For example, the Greek technique of “application of area” (see below Greek mathematics) corresponded to the Babylonian quadratic methods (although in a geometric, not arithmetic, form). Further, the Babylonian rule for estimating square roots was widely used in Greek geometric computations, and there may also have been some shared nuances of technical terminology. Although details of the timing and manner of such a transmission are obscure because of the absence of explicit documentation, it seems that Western mathematics, while stemming largely from the Greeks, is considerably indebted to the older Mesopotamians.

Mathematics in ancient Egypt

The introduction of writing in Egypt in the predynastic period (c. 3000 bce) brought with it the formation of a special class of literate professionals, the scribes. By virtue of their writing skills, the scribes took on all the duties of a civil service: record keeping, tax accounting, the management of public works (building projects and the like), even the prosecution of war through overseeing military supplies and payrolls. Young men enrolled in scribal schools to learn the essentials of the trade, which included not only reading and writing but also the basics of mathematics.

One of the texts popular as a copy exercise in the schools of the New Kingdom (13th century bce) was a satiric letter in which one scribe, Hori, taunts his rival, Amen-em-opet, for his incompetence as an adviser and manager. “You are the clever scribe at the head of the troops,” Hori chides at one point,

a ramp is to be built, 730 cubits long, 55 cubits wide, with 120 compartments—it is 60 cubits high, 30 cubits in the middle…and the generals and the scribes turn to you and say, “You are a clever scribe, your name is famous. Is there anything you don’t know? Answer us, how many bricks are needed?” Let each compartment be 30 cubits by 7 cubits.

This problem, and three others like it in the same letter, cannot be solved without further data. But the point of the humour is clear, as Hori challenges his rival with these hard, but typical, tasks.

What is known of Egyptian mathematics tallies well with the tests posed by the scribe Hori. The information comes primarily from two long papyrus documents that once served as textbooks within scribal schools. The Rhind papyrus (in the British Museum) is a copy made in the 17th century bce of a text two centuries older still. In it is found a long table of fractional parts to help with division, followed by the solutions of 84 specific problems in arithmetic and geometry. The Golenishchev papyrus (in the Moscow Museum of Fine Arts), dating from the 19th century bce, presents 25 problems of a similar type. These problems reflect well the functions the scribes would perform, for they deal with how to distribute beer and bread as wages, for example, and how to measure the areas of fields as well as the volumes of pyramids and other solids.More From Britannicagenetics: Mathematical techniques

The numeral system and arithmetic operations

The Egyptians, like the Romans after them, expressed numbers according to a decimal scheme, using separate symbols for 1, 10, 100, 1,000, and so on; each symbol appeared in the expression for a number as many times as the value it represented occurred in the number itself. For example,  stood for 24. This rather cumbersome notation was used within the hieroglyp d²/h² (brackets indicate figures that 

The numeral system and arithmetic operations

Unlike the Egyptians, the mathematicians of the Old Babylonian period went far beyond the immediate challenges of their official accounting duties. For example, they introduced a versatile numeral system, which, like the modern system, exploited the notion of place value, and they developed computational methods that took advantage of this means of expressing numbers; they solved linear and quadratic problems by methods much like those now used in algebra; their success with the study of what are now called Pythagorean number triples was a remarkable feat in number theory. The scribes who made such discoveries must have believed mathematics to be worthy of study in its own right, not just as a practical tool.

The older Sumerian system of numerals followed an additive decimal (base-10) principle similar to that of the Egyptians. But the Old Babylonian system converted this into a place-value system with the base of 60 (sexagesimal). The reasons for the choice of 60 are obscure, but one good mathematical reason might have been the existence of so many divisors (2, 3, 4, and 5, and some multiples) of the base, which would have greatly facilitated the operation of division. For numbers from 1 to 59, the symbols  for 1 and  for 10 were combined in the simple additive manner (e.g.,      represented 32). But to express larger values, the Babylonians applied the concept of place value. For example, 60 was written as , 70 as  , 80 as   , and so on. In fact,  could represent any power of 60. The context determined which power was intended. By the 3rd century bce, the Babylonians appear to have developed a placeholder symbol that functioned as a zero, but its precise meaning and use is still uncertain. Furthermore, they had no mark to separate numbers into integral and fractional parts (as with the modern decimal point). Thus, the three-place numeral 3 7 30 could represent 31/8 (i.e., 3 + 7/60 + 30/60²), 1871/2 (i.e., 3 × 60 + 7 + 30/60), 11,250 (i.e., 3 × 60² + 7 × 60 + 30), or a multiple of these numbers by any power of 60.

The four arithmetic operations were performed in the same way as in the modern decimal system, except that carrying occurred whenever a sum reached 60 rather than 10. Multiplication was facilitated by means of tables; one typical tablet lists the multiples of a number by 1, 2, 3,…, 19, 20, 30, 40, and 50. To multiply two numbers several places long, the scribe first broke the problem down into several multiplications, each by a one-place number, and then looked up the value of each product in the appropriate tables. He found the answer to the problem by adding up these intermediate results. These tables also assisted in division, for the values that head them were all reciprocals of regular numbers.

Regular numbers are those whose prime factors divide the base; the reciprocals of such numbers thus have only a finite number of places (by contrast, the reciprocals of nonregular numbers produce an infinitely repeating numeral). In base 10, for example, only numbers with factors of 2 and 5 (e.g., 8 or 50) are regular, and the reciprocals (1/8 = 0.125, 1/50 = 0.02) have finite expressions; but the reciprocals of other numbers (such as 3 and 7) repeat infinitely  and , respectively, where the bar indicates the digits that continually repeat). In base 60, only numbers with factors of 2, 3, and 5 are regular; for example, 6 and 54 are regular, so that their reciprocals (10 and 1 6 40) are finite. The entries in the multiplication table for 1 6 40 are thus simultaneously multiples of its reciprocal 1/54. To divide a number by any regular number, then, one can consult the table of multiples for its reciprocal.

An interesting tablet in the collection of Yale University shows a square with its diagonals. On one side is written “30,” under one diagonal “42 25 35,” and right along the same diagonal “1 24 51 10” (i.e., 1 + 24/60 + 51/60² + 10/60³). This third number is the correct value of Square root of√2 to four sexagesimal places (equivalent in the decimal system to 1.414213…, which is too low by only 1 in the seventh place), while the second number is the product of the third number and the first and so gives the length of the diagonal when the side is 30. The scribe thus appears to have known an equivalent of the familiar long method of finding square roots. An additional element of sophistication is that by choosing 30 (that is, 1/2) for the side, the scribe obtained as the diagonal the reciprocal of the value of Square root of√2 (since Square root of√2/2 = 1/Square root of√2), a result usef