Note F — Chapter III
Reading edition
All the heights given, other than those taken from the Ordnance Survey, are deduced from observations made with a novel and portable form of mercurial barometer, which can be coiled up and carried in a small tin box in the pocket. As we were unable to make comparative readings with a second instrument at a known height, the barometrical readings are, in every case, calculated from the pressure at sea-level being assumed to be 30 inches. This makes the heights, as a rule, about 800 feet lower than if 31 inches were taken as the normal sea-level pressure.