It may also be remarked that, in striking out two ciphers at the end of the given numbers, they have been, at the same time, both of them divided by 100; for it follows from article 31, that in striking out 1, 2, or 3 ciphers on the right of any number, the number is divided by 10, or 100, or 1000, &c. 48. Division and multiplication mutually prove each other, like subtraction and addition; for, according to the definition of division (36), we ought, by dividing the product by one of the factors, to find the other, and multiplying the divisor by the quotient, we ought to reproduce the dividend (37). Fractions. 49. DIVISION cannot always be performed, so as not to leave a remainder, because every number of units is not exactly composed of any other number whatever of units, taken a certain number of times. Examples of this have already been seen in the table of Pythagoras, which contains only the product of the 9 first numbers multiplied two and two, but does not contain all the numbers between 1 and 81, the first and last numbers in it. The method hitherto given shows, then, only how to find the greatest multiple of the divisor, that can be contained in the dividend. If we divide 939 by 8, according to the rule in article 46, we have for the last partial dividend, the number 79, which does not contain 8 exactly, but which, falling between the two numbers, 72 and 80, one of which contains the divisor, 8, nine times, and the other ten, shows us that the last part of the quotient is greater than 9, and less than 10, and consequently, that the whole quotient is between 29 and 30. If we multiply the unit figure of the quotient, 9, by the divisor, 8, and subtract the product from the last partial dividend, 79, the remainder, 7, will evidently be the excess of the dividend, 239, above the product of the factors, 29 and 3. Indeed, having, by the different parts of the operation, subtracted successively from the dividend, 239, the product of each figure of the quotient by the divisor, we have evidently subtracted the product of the whole quotient by the divisor, or 232; and the remainder, 7, less than the divisor, proves, that 232 is the greatest multiple of 8, that can be contained in 239. 50. It must be perceived, after what has been said, that to reproduce any dividend, we must add to the product of the divisor by the quotient, the sum which remains when the division cannot be performed exactly. 51. If we wished to divide into eight equal parts a sum of whatever nature, consisting of 239 units, we could not do it without using parts of units or fractions. Thus, when we have taken from the number 239 the 8 times 29 units contained in it, there will remain 7 units, to be divided into 8 parts; to do this, we may divide each of these units, one after the other, into 8 parts, and then take one part out of each unit, which will give 7 parts to be joined to the 29 whole units, to form the eighth part of 239, or the exact quotient of this number, by 8. The same reasoning may be applied to every other example of division in which there is a remainder, and in this case the quotient is composed of two parts; one, consisting of whole units, while the other cannot be obtained until the concrete or material units of the remainder have been actually divided into the numArith. 5 ber of parts denoted by the divisor; without this it can only be indicated by supposing, a unit of the dividend to be divided into as many parts as there are units in the divisor, and so many of these parts, as there are units in the remainder, taken to complete the quotient required. 52. In general, when we have occasion to consider quantities less than unity, we suppose unity divided into a certain number of parts sufficiently small to be contained a certain number of times in these quantities, or to measure them. In the idea thus formed of their magnitude there are two elements, namely, the number of times the measuring part is contained in unity, and the number of these parts found in the quantities. A nomenclature has been made for fractions, which answers to this manner of conceiving and representing them. That which results from the division of unity into 2 parts is called a moiety or half, and so on, adding after the two first, the termination th to the number, which denotes how many parts are supposed to be in unity. Every fraction then is expressed by two numbers; the first, which shows how many parts it is composed of, is called the numerator, and the other, which shows how many of these parts are necessary to form an unit, is called the denominator, because the denomination of the fraction is deduced from it. Five sixths of an unit is a fraction, the numerator of which is five, and the denominator six. The numerator and the denominator together are called the two terms of the fraction. Figures are used to shorten the expression of fractions, the denominator being written under the numerator, and separated from it by a line, one third is written, 53. According to the meaning attached to the words, numerator and denominator, it is plain, that a fraction is increased, by increasing its numerator without changing its denominator; for this last, as it shows into how many parts unity is divided, determines the magnitude of these parts, which continues the same, while the denominator remains unchanged; and by augmenting the numerator, the number of these parts is augmented, and consequently the fraction increased. It is thus, for instance, that exceeds, and that 13 exceeds 11: It follows evidently from this, that by repeating the numerator 2, 3, or any number of times, without altering the denominator, we repeat, a like number of times, the quantity expressed by the fraction, or in other words multiply it by this number; for we make 2, 3, or any number of times, as many parts, as it had before, and these parts have remained each of the same value. The fraction, then, is the triple of 1 and 10 the double of A fraction is diminished by diminishing its numerator, without changing its denominator, since it is made to consist of a less number of parts than it contained before, and these parts retain the same value. Whence, if the numerator be divided by 2, 3, or any number, without the denominator being altered, the fraction is made a like number of times smaller, or is divided by that number, for it is made to contain 2, 3, or any number of times less parts than it contained before, and these parts remain of the same value. Thus is a third of and is half of 54. On the contrary, a fraction is diminished, when its denominator is increased without changing its numerator; for then more parts are supposed in an unit, and consequently they must be smaller, but, as only the same number of them are taken to form the fraction, the amount in this case must be a less quantity than in the first. Thus is less than, and than 3. Hence it follows, that if the denominator of a fraction be multiplied by 2, 3, or any number, without the numerator being changed, the fraction becomes a like number of times smaller, or is divided by that number, for it is composed of the same number of parts as before, but each of them has becomes 2, 3, or a certain number of times less. The fraction is half of, and the third of . A fraction is increased when its denominator is diminished without the numerator being changed; because, as unity is supposed to be divided into fewer parts, each one becomes greater, and their amount is therefore greater. Whence, if the denominator of a fraction be divided by 2, 3, or any other number, the fraction will be made a like number of times greater, or will be multiplied by that number for the number of parts remains the same, and each one becomes 2, 3, or a certain number of times greater than it was before. According to this, is triple of and the quadruple of It may be remarked, that to suppress the denominator of a fraction is the same as to multiply the fraction by that number. For instance, to suppress the denominator 3 in the fraction is to change it into 2 whole ones, or to multiply it by 3. 55. The preceding propositions may be recapitulated as follows; By multiplying the numerator, the fraction is By multiplying the denominator, the fraction is S multiplied, divided. S divided, multiplied. { 56. The first consequence to be drawn from this table is, that the operations performed on the denominator produce effects of an inverse or contrary nature with respect to the value of the fraction. Hence it results, that, if both the numerator and denominator of a fraction be multiplied at the same time, by the same number, the value of the fraction will not be altered; for if, on the one hand, multiplying the numerator makes the fraction 2, 3, &c. times greater, so on the other, by the second operation, the half or third part, &c. of it is taken; in other words, it is divided by the same number, by which it had at first been multiplied. Thus is equal to, and is equal to 19. 10 57. It is also manifest that, if both the numerator and denominator of a fraction be divided, at the same time, by the same number, the value of the fraction will not be altered ; for if, on the one hand, by dividing the numerator the fraction is made 2, 3, &c. times smaller; on the other, by the second operation, the double, |