NEPER’S RODS. 
vented hy llie above-named person, where- 
by the multiplication and division of large 
numbers are, much facilitated. 
As to the Constructinn of Neper's Rods : 
suppose the common table of multiplica- 
tion to lie made upon a plate of metal, ivo- 
ry, or paste-board, and then conceive the 
several columns (standing downwards from 
the digits on the head) to be cut asunder ; 
and these are what we call Neper’s rods for 
multiplication. But then there must be a 
good number of eacii ; for as many times 
as any figure is in the multiplicand, so many 
rods of that species (i. e. with that figure 
on the top of it) must we have; though six 
rods of each species will be sufficient for 
any example in common affairs: there must 
also be as many rods of O's. 
But before we explain the way of using 
these rods, there is another thing to be 
known, vk. that the figures on every rod 
are written in an order different from that 
in the table. Thus, the little square space, 
or division, in which the several products of 
every column are written, is divided into 
two parts by a line across, from the upper 
angle on the right to the lower on the left ; 
and if the product is a digit, it is set in the 
low'er division ; if it has two places, the 
first is set in the lower, and the second in 
the upper division ; but the spaces on the 
top are not divided; also there is a rod of 
digits, not divided, which is called the in- 
dex rod, and of this we need but one single 
rod. 
Multiplication by Neper's Rods. First lay 
down the index rod ; then on the right of 
it set a rod, whose top is the figure in the 
highest place of the multiplicand : next to 
this again, sfet the rod whose top is the next- 
figure of the multiplicand; and so on in or- 
der, to the first figure. Then is your mul- 
tiplicand tabulated for all the nine digits ; 
for in the same line of squares standing 
against every figure of the, index-rod, you 
have the product of that figure, and there- 
fore you have no more to do but to transfer 
the products and sum them. But in taking 
out tliese products from the rods, the order 
in which the figures stand obliges you to a 
very easy and small addition: thus, begin 
fo take out the figure in the lower part, or 
unit’s place, of the square of the first rod 
on the right : add the figure in the upper 
jiart of this rod to that in the lower part of 
the next, and so on, which may be done as 
fast as you can look on them. To make 
this practice as clear as possible, take the 
following example. 
Example. To midfqdy 4,768 by 18.1. 
Having set the rods togetlier for the num- 
ber 4,768, against h in the index, I find 
this number, by adding according to the 
Against 8, this number 33 ^44, 
Against 3, this number 14,304 
Total product 1,835,680 
To make the use of the rods yet more 
regular and easy; they are kept in a flat, 
square box, whose breadth is that of ten 
rods, and the length that of one rod, as 
thick as to hold six (or as many as you 
please) the capacity of the box being di- 
vided info ten cells, for the different '’spe- 
cies of rods. When the rods are put up in 
the box, (each species in its own cell dis- 
tinguished by the first figure of the rod set 
before it on the face of the box near the 
top) as much of every rod stands without 
the box as shews the first figure of that 
rod ; also upon one of the flat sides without 
and near the edge, upon the left hand, the 
index-rod is fixed : antf along the foot there 
is a small ledge, so that the rods, when ap- 
plied, are laid upon this side, and supported 
by the ledge, which makes the practice 
very easy ; but in case the multiplicand 
should have more than nine places, that up- 
per face of tfie box may be made broader. 
Some make the rods with four different 
faces, and figures on each for different pur- 
poses. 
Division by Neper's Rods. First tabulate 
your divisor; then you have it multiplied 
by all the digits, out of which you may 
choose such convenient divisors as will be 
next less to the. figures in the dividend, and 
write the index answering in the quotient, 
and so continually, till the work is done. 
Thus 2,17f»,788, divided by 6,123, gives in 
the quotient 356. 
Having tabulated the divisor, 6,123, you 
see that 6,123 cannot be had in 2,179 ; there- 
fore take five places, and on the rods find a 
number that is equal, or next less to 21,797, 
which is 18,369 ; that is, three times the di- 
visor, wherefore set 3 in the quotient, and 
subtract 18,369 from the figures above, and 
there will remain 3,428 ; to which add 8, 
the next figure of the dividend, and seek 
again on the rods for it, or the next less, 
which you will find to be five times ; there- 
fore set 5 in the quotient, and subtract 
30615 from 34,228, and there will remain 
3,673, to which add 8, the last figure in the 
dividend, and finding it to be just six times 
the divisor, set 6 in the quotient, 
