Explanation of the Difference Engine.
Those who are only familiar with ordinary arithmetic may, by following out with the pen some of the examples which will be given, easily make themselves acquainted with the simple principles on which the Difference Engine acts.
It is necessary to state distinctly at the outset, that the Difference Engine is not intended to answer special questions. Its object is to calculate and print a series of results formed according to given laws. These are called Tables—many such are in use in various trades. For example —there are collections of Tables of the amount of any number of pounds from 1 to 100 lbs. of butchers' meat at various prices per lb. Let us examine one of these Tables: viz.—the price of meat 5d. per lb., we find
| Number. | Table. | |
| Lbs. | Price. | |
| s. | d. | |
| 1 | 0 | 5 |
| 2 | 0 | 10 |
| 3 | 1 | 3 |
| 4 | 1 | 8 |
| 5 | 2 | 1 |
There are two ways of computing this Table:—
1st. We might have multiplied the number of lbs. in each line by 5, the price per lb., and have put down the result in l. s. d., as in the 2nd column: or,
2nd. We might have put down the price of 1 lb., which is 5d., and have added five pence for each succeeding lb.
Let us now examine the relative advantages of each plan. We shall find that if we had multiplied each number of lbs. in
