Page:Passages from the Life of a Philosopher.djvu/74

58 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:—

It will be observed that, in making this addition, the mind acts by successive steps. The person adding says to himself—

In the following addition there are several carriages:—

The person adding says to himself—

Now, the length of time required for adding one number to another is mainly dependent upon the number of figures to