_Answer._ As soon as it begins to grow dark, the head-light must be lighted and properly trimmed, and the proper lamp signals placed in front of the engine, if the rules of the road require the display of such signals. A lamp should always be placed in the cab, so as to throw its light on the steam-gauge, but not into the runner’s face, because he is unable to see distant signals so well if his eyes are exposed to the glare of a light near him. At night, as objects which are passed can not be seen distinctly, it is more difficult to tell the speed at which an engine is running than it is in the day time. A runner should therefore consult his watch frequently, and by counting the revolutions of the wheels, which he can do by the sound of the pump valve or other part of the machinery, he can tell from the rule given in the answer to Question 438 the speed at which the locomotive is running. From this rule a table can easily be constructed for an engine with any size of driving-wheels, showing the speed for any given number of revolutions per minute. It will be a good exercise for a young locomotive runner to construct such a table, which will be found very convenient for reference if placed in a conspicuous place in the cab. QUESTION 488. _What must be attended to in very cold weather?_ _Answer._ Great care must be exercised to prevent the water in the pumps, pipes and in the tender from freezing. If it does it will be almost certain to break the pump or burst the pipes. To avoid this the heater cocks must be opened so as to keep the water in the tender warm. In excessively cold weather the engine should be run with greater caution than at other times, as iron is then more brittle, and also more liable to break, owing to the frozen condition and consequent solidity of the track. QUESTION 489. _In running a locomotive in severe snow or rain-storms, what should be observed?_ _Answer._ Whenever it snows the pilot or cow catcher should be covered with boards, or, better still, with sheet iron, so as to act like a snow plow. Brooms made of steel wire should be placed in front of the front wheels of the engine, so as to sweep the snow from the rails. The front damper on the ash-pan should be kept closed so as to exclude the snow from the ash-pan, which would soon fill it up, and in this way obstruct the draft. If the fall of snow is very heavy or it blows into drifts, the train must of necessity run very slowly, and even if a part of the track is clear of snow, it is unsafe to run fast on it, as there would be danger of throwing the engine off the rails if it should run into a heavy drift at a high speed. In severe rain storms bridges, culverts and such portions of the track as are liable to be washed away should be approached cautiously, especially at night. In both snow and rain-storms, and also in fogs, great caution is required, owing to the difficulty of seeing signals. QUESTION 490. _What is meant by a reserve engine or_ “_helper?_”