NAPIER'S BONES, or RODS, a contrivance of Napier to facilitate , the performance of multiplication and division, explained by him in his' Itabdologile, eeu nummtionis per virgules libri duo,' Edinburgh, • 1617, 12ino. The invention would have been perhaps more employed, Several of the above compounds exist in seven, or less, distinct modifi cations; Laurent, the completeness of whose researches on these bodies is only equalled by their importance, accounts for this fact by supposing that each of the eight equivalents of hydrogen in naphthalin has its allotted position, and that according as one or other is replaced by the chlorine or the bromine so do the properties of the resulting compound differ.
In naming the many derivatives of naphthalin, Laurent adopted the word naplit as the root, prefixing it by dela, bra, &c., to indicate the substituting element ; and introducing the vowels, a, e, a, u, when it was necomry to show that one, two, three, four, or five atoms of the clement had been taken into tho compound molecule. When more than five replacing atoms were employed, the syllable al was intro duced, and the use of the vowels recommenced. Numerous examples of this useful, though scarcely euphonical, nomenclature will be observed throughout the article.
The second class of chlorine and bromine derivatives of naphthalin are combinations of the compounds just described, with additional equivalents of chlorine or bromine, ordinary chlorides and bromides resulting. They are nearly all formed by the direct action of chlorine or bromine upon the different naphthaline. When acted upon by alcoholic solution of potash, they are split up into hydrochloric or hydrobromio acids, and the chlor- and brom.naphthalins already mentioned. The following is a list of these chlorides and bromides of naphthalin, or of its derivatives :— but for his discovery of logarithms ; and even yet it might be used with advantage by young arithmeticians in verification of their work.
We shall therefore describe it, with a very slight modification, which somewhat facilitates its use.
The preceding cut represents one of the rods belonging to the number 3. It is a parallelogram with an angle of 45°, containing nine equilateral parallelograms, with one vertical diagonal in each. In these are distributed, in a manner which will be visible at a glance, the multiples cf the number which stands at the head, up to nine times. A sufficient number of rods must be provided for each of the headings 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, so that by placing the proper rods side by side, any nmober may be seen at the head, as in the following diagram, which represents rods in juxtaposition ready for the multiplication of 709958.
These may be added on the rods, and the result 5679664 written down In its proper place. The same is done with the other digits, and the results are added in the usual manner.
The only difference between the preceding description and Napier's rods is, that in the latter the rods are upright, and the additions that are made from the rods are therefore made diagonally. The compart ments should be made large enough to allow of the figures which are to Ift added standing directly under one another. They represent a method on paper of the Ilindoo arithmeticians, of which Napier knew nothing.
Napier's bones, as they were called, have been much more often described in historical works than in those intended for use. Sir Walter Scott must have had an indistinct remembrance of them, with out however knowing what the phrase meant, when he made Davie Ramsay, in the ' Fortunes of Nigel,' swear by " the bones of the immortal Napier."