Properties of logarithms enable calculations to be conducted by simpler operations, provided the logarithms and antilogarithms are available for consultation from tables or by a mechanical slide rule or similar device if not by computation. A logarithm of a multiple of two quantities is the sum of their logarithms. This enables multiplication calculations to be reduced to addition. A logarithm of a fraction is the difference between the logarithms of its numerator and denominator, enabling division to be replaced by mere subtraction followed by conversion of the result to the power term by the antilogarithm or exponentiation. It follows from these rules that the logarithm of a composite whole number can be reduced to a sum of multiples of the logarithms of its prime factors, and indeed the logarithm of any rational number can be decomposed into addition and subtraction of multiples of the logarithms of the prime factors of the numerator and denominator of the fraction. Furthermore, logarithms can be used for calculating irrational numbers that result from algebraic operations on rational numbers. A rational number can be raised to any fractional power by applying a logarithm, which can then be manipulated by the rules of logarithms to provide the fraction multiplied by the logarithm of the rational number. For example, the rational number three to the power the fraction a half is the same as the irrational square root of three and can be calculated with the aid of logarithms by taking the logarithm of it to any base, resulting in half the logarithm of the prime number three to that base. That result is then converted from a logarithm to a power term by exponentiation to furnish the square root of three to an accuracy of the number of significant figures allowed by the logarithms and antilogarithms available.
While the rules of logarithms apply no matter what consistent positive real base they have, it is clear that logarithms would be especially useful if the base chosen were one such that the logarithms of the simplest prime numbers to that base were approximated peculiarly well by a limited number of significant figures of their logarithms. Unfortunately, logarithms are usually transcendental irrational numbers that cannot be exactly represented by terminating strings of numerals in positional notation. Nevertheless, sometimes the logarithm of a number such as a prime number can be approximated well enough to a few significant figures, which would make arithmetic with them involve fewer steps and be faster. For example, if the base of the logarithms is chosen to be close to a root of the prime number two whereby two is raised to the power of a unit fraction or reciprocal of a counting number, then raising that irrational base to the power of that counting number will result nearly in the prime number two with the consequence that the logarithm of two to that irrational root base will be nearly a whole number capable of being represented by a finite number of significant figures. The creation of such a root of two as a base is equivalent to a temperament of the musical octave into equal geometric steps, with the ratio between the frequencies of adjacent notes a step apart being the base of the logarithms. The task of finding a base of logarithms such that the logarithms of the smallest prime numbers are approximated very well by terminating numbers is hence equivalent to finding temperaments of the octave that align with the frequencies of the first prime numbers as harmonics.
A number of temperaments of the octave are already known to provide good coincidences with the first few harmonics. The most widespread is the equal temperament of the octave into twelve semitones, which corresponds well with the harmonics that are powers of the prime numbers two or three, and to lesser accuracy the prime number five. Other temperaments can approximate more of the small prime numbers. For example, temperament of the octave into six dozen equal step notes can provide good enough approximation to the first few smallest prime numbers two, three, five, seven, and eleven. Since the twelve semitones are a subset of these six dozen steps and six dozen is half the second power of twelve, temperament of the octave by a power of base twelve is particularly useful for music and would be good as a base of logarithms for mathematical calculations. While there is little wrong with temperament of the octave into six dozen steps in music, a slight annoyance could arise with this formulation of the base of logarithms mathematically because there are two bases involved: binary, the logarithm to the base of which gives the number of octaves, and dozenal for writing the logarithms in numerals and expressing the number of steps within the octaves, but just one base for the number of different numerals and for the base of the logarithms and all computation would rather be desired. Is there a way to have the same base for the base of the logarithms and for the number of different digits by which the logarithms are notated? The answer is almost.
If the problem is approached initially by finding base B such that B^(1/B) is nearly the frequency ratio of the step in the octave desired, then the same base can be used as the base of the logarithms and as the number of different numerals for notating numbers such that the logarithms will tell the number of those steps, but the logarithms will not necessarily round well at the octaves to powers or whole number multiples of that base B. It so happens that the temperament to six dozens steps per octave is approximated when the base B is the square or second power of twenty-six. A base for the logarithms can be constructed by sectioning the square of twenty-six into twenty-six steps geometrically. The logarithms of the smallest prime numbers two, three, and five to that step as base, which is equivalent to half the logarithms to the base twenty-six, will be particularly accurate to two significant figures when written in base twenty-six. The logarithm of the prime number seven to this base is not as accurate at just two significant figures. Thus, computations using logarithms of numbers containing the first three prime numbers would be unusually convenient in base twenty-six, which could be called base two dozen plus two or twenzy-two in another form of dozenal parlance. There are as many upper case letters in the modern English variety of the Roman alphabet to use as symbols for the numerals for this base.
More accurate results for the logarithms of also the next prime numbers seven and eleven can be had to two significant figures by base thrice eleven, using a third of the logarithm to that base. There are said to be as many runes in the English futhorc as the number of different numerals required for this base thrice eleven. However, apart from such a base being an odd one to use for general purposes in society, like base twenty-six it would not round to whole multiples for the number of steps at the octaves.
Is there a way to allow the numbers of temperament steps at the octaves to be round multiples of the base? This is possible if the step size for the base of the logarithms can be defined in terms of powers of the number of equal temperament steps per octave. To make that number of steps a convenient base to use, it is made to be a power of twelve, either twelve itself or its square. For a step near two to the power of a square twelfth, the square of thrice thirteen is close to the base in B^(1/B) required for the logarithms, but the logarithm of two is not as accurate to two significant figures and the notation would have to be in base twelve for the numbers of steps at the octaves to be rounded.
More conveniently, the base of the logarithms for the semitone is given nearly by the cubic dozenth root of twelve to the power of forty. When such logarithms are written in base twelve, there are few significant figures to a good degree of accuracy for the first few prime numbers. The prime number seven requires more significant figures for a not worse level of accuracy, but they are not too many to be useful in approximate calculations. These logarithms give approximations for the numbers of semitones for the harmonics, which are easy to remember when musical theory is understood. These logarithms are defined in terms of powers only of the base twelve and can be reduced to simple arithmetic using the base twelve logarithms.
It should be mentioned that the fortieth root of ten also nearly gives the semitone step, but expressed that way the base of the logarithms and the base of numeration to allow rounded numbers of semitones at the octaves for this to be useful in conjunction with musical theory are not the same. The common decimal logarithms of the smallest prime numbers two, three, and five are accurate enough to two significant figures if multiplied by forty or four. A thousand to the power of a hundredth partitions the octave into ten equal steps. Not many useful bases B have that property of having whole number values of n and m to make B^(n/B^m) partition the octave into nearly B steps. Binary bases, decimal, and dozenal do. The dozenal option that I have described has the extra benefits of giving accurate values for the logarithms of the first few prime numbers by a small number of significant figures and agreeing well with the most normal musical temperament.




