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Aneroid Barometers: Determining Altitudes

wo instruments (aneroid barometers) were in use in the field, one for observing the altitudes and the other in reserve in case of emergency and for detecting errors of a physical character in the instruments in use.

One day’s work will suffice to illustrate the method of recording the observations and corrections made for determining the altitude. A start is made at some point, the altitude of which, above sea level, is already known and carefully recorded by the aneroid a few hours before starting. Another observation is made by the same instrument at the same spot when starting, the difference of the two readings giving any local variation. The practice was to take observations of local variations every few hours, usually at meal hours. If the weather appeared unsettled, a rest of half an hour between meal hours was often found to be time well spent on the journey. Observations were always made on retiring at night, on rising in the morning, on starting out for the day and on arriving at the next camping place in the evening.

Records of observations: The accompanying blank form will illustrate the system used for recording aneroid observations in the field book and afterward reducing them to sea level. By carefully studying the fluctuations of the barometer during the day the corrections for each observations were determined by interpolation and entered in the column for “Corrected barometric readings.” The difference between the corrected reading and sea level, which was determined at the start, or wherever available during the progress of the work, was added or subtracted, as the case might be, and the results entered in the column for “Elevations above sea level.” The condensed profiles which accompanied the reconnaissance reports were afterward prepared from the elevations above sea level. These profiles [were] pieced together to form the continuous profile, and cover a distance of more than 700 miles.

Source: J.G. MacGregor, Canadian Railway and Marine World, September, 1914.