_Answer._ A _reserve engine_ is a locomotive which is not employed in hauling a regular train, but is kept as a “reserve” to go to the help of an engine which may be compelled to stop on account of an accident of any kind, or to assist engines in moving trains up heavy grades, or is used in clearing away a wrecked train, rebuilding bridges or other structures. QUESTION 491. _What must be observed in running a reserve engine?_ _Answer._ As no special arrangements are usually made in preparing time-tables[110] for the running of reserve, or as they are usually called by railroad men, “_wild_” engines, it may very probably happen that it will be called upon to assist other engines when the road is not clear, and therefore its runner must constantly be on the look-out for signals to stop, which are often given suddenly. He must switch off with special caution in order to be sure to keep out of the way of regular trains running in the opposite direction on the same track. When he reaches the train or place where the assistance of the reserve engine is needed, he must approach it _slowly_ and _carefully_, in order to avoid a violent shock. On the return from the assisted train, he incurs the same danger, and must pay close attention to any signal to stop made to him by any opposite train on the same track, and also on his part warn such trains by the proper signals. [110] A _time-table_ is a table which gives the time when each train shall arrive at the stations it passes, the stations at which it shall stop, and all the regulations by which it shall be run. When a train is run with two engines, both in front of it, the forward one always takes the management of the train. The runner of the hind engine must be guided by the signals of the runner of the forward engine. In starting, the forward engine must be set in motion first and then the one behind it. In stopping, the steam must be shut off first in the hind engine. Likewise in decreasing the speed during the trip, the hind engine must first regulate the flow of steam. If these precautions are not observed the forward engine may easily be thrown from the track by the faster motion of the hind one. When a train is assisted by a “helper” placed _behind_ the train, and therefore pushing it, the forward engine must likewise be set in motion first, and steam should be let on in the hind engine only after a signal has been given by the runner of the head engine. During the run both engines must move with the same speed.[111] [111] Katechismus der Einrichtung und des Betriebes der Locomotive, by Georg Kosak. QUESTION 492. _How should switching engines be managed?_