我又來翻譯了

The course of a railway train is uniquely prescribed for it at most points
of its journey by the rails on which it runs.Here and there, however, it
comes to a junction at which alternative courses are open to it, and it
may be turned on to one or the other by the quite negligible expenditure
of energy involved in moving the points.

鐵路火車是完全依循鐵軌上的道岔，來跑出它的路線。
然而，鐵軌上某些地方會出現交叉口，可以通往不同的
路線。在這些交叉口上，我們只需要微不足道的電力，
打開某個開關，就可以移動道岔，讓火車跑出不同的路線來。