On the relation between barometric pressure and the water-level in a well at Kew Observatory, Richmond

Abstract

The investigation which forms the subject of the present communication must be regarded as forming part of a general inquiry into the mode of action of the well at Kew Observatory, Richmond. The well was sunk during the course of some extensive alterations to the building about four years ago, and the water-level has been continuously recorded since the end of July, 1914. The mean level for each day expressed in centimetres above Ordnance Datum has been published in the ‘ Geophysical Journal,’ and the extreme values for each month have usually been given in the Monthly Weather Report. After being in action for two years, it was thought desirable to undertake a somewhat detailed examination of the records which had accumulated. The most interesting feature of the inquiry proved to be the periodic variations of, level, which were to be attributed to the tidal oscillations of the neighbouring River Thames. The most noteworthy response of the well was found in the case of the lunar fortnightly oscillation, which could, indeed, be plainly seen by merely plotting successive daily mean levels on a fairly open scale. The solar and lunar diurnal, semi-diurnal, ter-diurnal, ..., oscillations were sought for by forming solar and lunar diurnal inequalities at two-hour intervals and analysing the resultant variations. During the course of this work, it soon became evident that the extent of the solar diurnal variation was very much greater than one had any right to expect, and one inferred, that the solar tides were not alone concerned in its production. The effect of barometric pressure suggested itself as a likely factor, and an investigation was accordingly taken in hand.