execution, little beyond mechanical means of performing the arithmetical operation of Addition. Subtraction can, by the aid of a well-known artifice, be converted into Addition.
The process of Addition includes two distinct parts—1st. The first consists of the addition of any one digit to another digit; 2nd. The second consists in carrying the tens to the next digit above.
Let us take the case of the addition of the two following numbers, in which no carriages occur:—
6023
1970
——
7993
It will be observed that, in making this addition, the mind acts by successive steps. The person adding says to himself—
0 and 3 make three,
7 and 2 make nine,
9 and 0 make nine,
1 and 6 make seven.
In the following addition there are several carriages:—
2648
4564
——
7212
The person adding says to himself—
| 4 and 8 make 12 : | put down 2 and carry one. |
| 1 and 6 are 7 and 4 make 11 : | put down 1 and carry one. |
| 1 and 5 are 6 and 6 make 12 : | put down 2 and carry one. |
| 1 and 4 are 5 and 2 make 7 : | put down 7. |
Now, the length of time required for adding one number to another is mainly dependent upon the number of figures to
