BONES

An instrument contrived by the celebrated Lord Napier, the inventor of the logarithms, for the purpose of performing mechanically the arithmetical operations of multiplication and division. Napier's rods consist of small squared pieces of bone or ivory, box or silver, about 3 inches long, and 3-lOths of an inch in breadth, the faces of which are divided into nine little squares or cells, each of which is parted by a diagonal into two triangles. On these cells are engraved the succe ive columns of the common multiplication table, in such a manner that the units, or right-hand figures, are found in the right-hand triangle, and the tens, or left-hand figures, in the left-hand triangle. Thus: — As an example of the manner in which the rods are used, let it be required to multiply the numbers 6795 by 4876. Select the rods which have the figures of the multiplicand inscribed at the top, and place them in their order, with the index rod before them, when they will stand as in the table annexed. Then, opposite to the several figures of the multiplier, 4876, on the index, but proceeding backwards, take the numbers in each horizontal column; add the pair of digits in each rhombus formed by the adjacent triangles of two contiguous cell's; and, finally, collect into one sum the rows of the products corresponding to each digit of the multiplier, transcribed and properly disposed, asunder:— 40770 47565 54360 27180 33132420 Here, opposite to 6, the last digit of the multiplier, and proceeding from the right along the horizontal column, 805 NARCEIA. there occur the figures — first, 0, then 3 and 4, or 7; 5 and 2, or 7; 4 and 6, or 10; and lastly, writing down the cipher, and carrying 1 to the 3, we get 4. These collected together give 40770 for the product of 6795 by 6. In the same manner the other rows are formed, which, being added in the usual manner, the product of the two given numbers is obtained. It is obvious that this method of calculation is much too tedious to be of any real use. [s. 818]