(3) Concrete illustrations.
Problem: To find the weight of coal.
| Antecedents | Consequents | ||||||
| Weight of driver, |  | = | 4200 lbs. | ||||
| Weight of wagon, | |||||||
| Weight of coal. | |||||||
| Weight of driver, | | = |  | 200 lbs. | | = 2200 lbs. | |
| Weight of wagon. | 2000 lbs. | ||||||
Hence we may conclude that the weight of coal is 4200 lbs. − 2200 lbs., or 2000 lbs.
Perhaps the most noted instance in history of the application of this method, was the one which resulted in the discovery of Neptune. In calculating the orbit of Uranus, it was found that the combined attractions of the sun and the known planets did not account for the path which Uranus took. There was some unknown influence at work. Assuming that this unaccountable attraction was due to the presence of another planet beyond the orbit of Uranus, an Englishman by the name of Adams, and later the Frenchman Leverrier, were able to indicate by the principle of Residues, the spot where this planet should be. By directing the telescope toward this point, Neptune was discovered.
(4) Distinguishing features:
The phenomenon always occurs,
The antecedents are usually invariable,
Some of the antecedents are known to be the cause of a part of the phenomenon.
(5) Advantages and disadvantages.