MARSH, E. A.—An important figure in watch manufacturing in America for a number of years. Born at Sunderland, Conn., in 1837, in 1863 he entered the employ of the Waltham Watch Company and rose to the position of General Superintendent. In 1908 he retired from active service but retains his connection with the company as consulting superintendent. Besides his practical services to the watchmaking industry Mr. Marsh wrote "The Evolution of Automat Machinery," in 1896. MASSEY, EDWARD—An English watchmaker of the early nineteenth century. He invented the "crank roller" escapement, a kind of keyless winding for watches, and many other watch parts. MEAN SOLAR DAY—The average length of all the solar days in a year. This period is divided into 24 parts, or hours. MEAN TIME—Clocks, watches, etc., are made to measure equal units of time instead of the apparent time indicated by the sun. Mean time and true solar time agree only four times in a year. See _Equation of Time_. MERCER'S BALANCE-A balance of the ordinary kind fitted with an auxiliary—a laminated arm of brass and steel fixed at one end to the central bar of the balance and on its free end carrying two adjustable screws. This auxiliary may be arranged for either extreme of temperature with great accuracy. [Illustration] MERIDIAN DIAL—A dial for determining when the sun is on the meridian. It is very simply constructed. For directions see "Watch and Clockmakers' Handbook," by F. J. Britten. MERIDIAN WATCH—A watch which shows the time in a number of places in different parts of the world. It is set to Greenwich time and marks the difference between this and the time of all the great metropolitan cities in both hemispheres. [Illustration] METRONOME—An instrument for indicating and marking exact time music. It consists of a counterbalanced, or reversed, pendulum, which may be regulated to swing at any desired number of vibrations per minute. MIDDLE TEMPERATURE ERROR—The compensation balance does not exactly meet the temperature error. The rim expands too much with decrease of temperature and contracts too little with the increase. Hence a watch or chronometer can be correctly adjusted for two points only. The unavoidable error between is the middle temperature error. MINUTE—The sixtieth part of a mean solar hour. MINUTE HAND—The hand on a clock or watch which indicates the minutes. In the earlier days clocks had no minute hand. It was first concentered with the hour hand in 1673. MINUTE WHEEL—The wheel which carries the minute hand and is driven by the cannon pinion. MINUTE WHEEL PIN OR STUD—The stud fixed to the plate on which the minute wheel pinion turns. MINUTE WHEEL PINION OR "NUT"—The pinion in watches on which the minute wheel is mounted and which drives the hour wheel.