WATCHING THE EXHAUST.
What the beating pulse is as an aid to the physician in diagnosing diseases, the sound of the exhaust is to the engineer as a means of enabling him to distinguish between perfective and defective working of the locomotive. The ability to detect a slight derangement by the sound of the exhaust, can only be acquired by practice in watching those steam-notes day after day, as they play their tune of labor through the smoke-stack. When the steam-ports are even, and the valves correctly set, with tight piston-packing, and valves free from leaks, the notes of the exhaust will sound forth in regular succession in sharp, ringing, clear tones, every puff seeming to cut the steam clean off at the top of the stack. There is a long array of defects represented in the journey from this case of apparently perfect steam performance, to that where the exhaust steam escapes as an unbroken roar mixed with uncertain, wheezy coughs.