MULTIPLICATION BY LOGARITHMS.

RULE.

TAKE out the logarithms of the factors from the table, then add them together, and their sum will be the logarithm of the product required. Then, by means of the table, take out the natural number, answering to the sum, for the product sought.

Observing to add what is to be carried from the decimal part of the logarithm to the affirmative index or indices, or else subtract it from the negative.

Also, adding the indices together when they are of the same kind, both affirmative or both negative; but subtracting the less from the greater, when the one is affirmative and the other negative, and prefixing the sign of the greater to the remainder.

DIVISION BY LOGARITHMS.

RULE.

FROM the logarithm of the dividend subtract the logarithm of the divisor, and the number answering to the remainder will be the quotient required.

Observing to change the sign of the index of the divisor, from affirmative to negative, or from negative to affirmative; then take the sum of the indices if they be of the same name, or their difference when of different signs, with the sign of the greater, for the index to the logarithm of the quotient.

And also, when 1 is borrowed, in the left-hand place of the decimal part of the logarithm, add it to the index of the divisor when that index is affirmative, but subtract it when negative; then let the sign of the index arising from hence be changed, and worked with as before.

Note. As to the Rule-of-Three, or Rule of Proportion, it is performed by adding the logarithms of the 2d and 3d terms, and subtracting that of the first term from their sum.

INVOLUTION

INVOLUTION BY LOGARITHMS.

RULE.

TAKE out the logarithm of the given number from the table. Multiply the log thus found, by the index of the power proposed. Find the number answering to the product, and it will be the power required.

Note. In multiplying a logarithm with a negative index, by an affirmative number, the product will be negative But what is to be carried from the decimal part of the logarithm, will always be affirmative. And therefore their difference will be the index of the product, and is always to be made of the same kind with the greater.

5850

Here 4 times the negative

index being-8, and 3 to carry,

the difference 5 is the index Power 5.14932*

of the product.

0.711750

This answer 5.14932 though found strictly according to the general rule, is not correct in the last two figures 32; nor can the answers to such questions relating to very high powers be generally found true to 6 places of figures by the table of logarithms in this work: if any power above the hundred thousandth were required, not one figure of the answer found by the table of logarithms here given could be depended on.

The logarithm of 1.0045 is 00194994108 true to eleven places, which multiplied by 365 gives 7117285 true to 7 places, and the corresponding number true to 7 places is 5'149067.

Voz: I.

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EVOLUTION

EVOLUTION BY LOGARITHMS.

TAKE the log. of the given number out of the table. Divide the log. thus found by the index of the root. Then the number answering to the quotient, will be the root.

Note. When the index of the logarithm, to be divided, is negative, and does not exactly contain the divisor, without some remainder, increase the index by such a number as will make it exactly divisible by the index, carrying the units borrowed, as so many tens, to the left-hand place of the decimal, and then divide as in whole numbers.

Ex. 1. To find the square root | Ex. 2. To find the 3d root of

Ex. 3. To find the 10th root | Ex. 4. To find the 365th root

ALGEBRA.

DEFINITIONS AND NOTATION.

ALGEBRA

LGEBRA is the science of computing by symbols. It is sometimes also called Analysis; and is a general kind of arithmetic, or universal way of computation.

2. In this science, quantities of all kinds are represented by the letters of the alphabet. And the operations to be performed with them, as addition or subtraction, &c, are denoted by certain simple characters, instead of being expressed by words at length.

3. In algebraical questions, some quantities are known or given, viz. those whose values are known and others unknown, or are to be found out, viz. those whose values are not known. The former of these arc represented by the leading letters of the alphabet, a, b, c, d, &c; and the latter, or unknown quantities, by the final letters, z, y, x, ù, &c.

4. The characters used to denote the operations, are chiefly the following:

+ signifies addition, and is named plus.

signifies subtraction, and is named minus.

or. signifies multiplication, and is named into.
signifies division, and is named by.

✔ signifies the square root;

4th root, &c; and the nth root.

::: signifies proportion.

the cube root; the

signifies equality, and is named equal to.

And so on for other operations.

Thus a + b denotes that the number represented by b is to be added to that represented by a.

ab denotes, that the number represented by b is to be subtracted from that represented by a.

a b denotes the difference of a and b, when it is not known which is the greater.

ab, or