Barometric Pressure in the Tropics

Abstract

THE American Eclipse Expedition to the Caroline Islands in May 1883 also made exceedingly interesting meteorological observations, of which the most important are those on the pressure of the air, as they elucidate some points in the daily period of this phenomenon (Memoirs of the National Academy of Sciences, vol. ii.). As this is very regular in the tropics, any difference in it points to exceedingly potent influences, and it is easy to surmise that, in the daytime, none, except a cyclone, can be more potent than an eclipse, as no other can shade the whole extent of the atmosphere. The result was an accelerated diminution of pressure from 10.15 to 11.30 am. (totality 11.32 to 11.37 am.), then a rise to about noon—i.e. at a time when there is generally a great fall—and later again an accelerated fall. The explanation is probably the following:—The accelerated fall at the beginning is caused by the diminished temperature and elasticity of the air. Then, as the height of equal pressure diminished in the shaded area, air began to flow in from the vicinity, causing a rise of pressure, and the subsequent rapid fall was a return to the normal condition.