Thus by the most correct adaptation of power, upon the above-named railroads, the following percentages of mileage may be saved.
| Massachusetts Western, | 70 |
| New York and Erie, | 55½ |
| Pennsylvania Central, | 68 |
| Baltimore and Ohio, | 75 |
Of these roads the Baltimore and Ohio is that which has actually the best adaptation; and the Western road of Massachusetts that which has the worst.
362. To determine the actual dimensions of the engines which should be used upon any road, from the tables, proceed as follows:—Let the load be one hundred tons, the maximum grade thirty feet per mile, and speed twenty-five miles per hour.
Referring to the tables in succession we have,
| By table 1, Traction for 100 tons, on a level, at 25 miles per hour, | 1,550 | lbs. |
| By table 2, Traction for 100 tons, on a 30 feet grade, | 1,273 | lbs. |
| Whole traction required, | 2,823 | lbs. |
By the formula, table 3, the weight upon the drivers must be
2823 × 6 = 16938 lbs., or 8 tons.
By table 4, with a wheel five feet in diameter, and a stroke of twenty inches, we have the decimal .2122.
By table 5, the mean cylinder pressure being sixty pounds per inch, and piston twelve inches in diameter, we have as the total pressure