The object of this investigation was to ascertain the differences of atmospheric pressure,reduced to sea-level, which accompany differences of temperature, as observed at the, High and the Low-Level Ben Nevis Observatories. The period of time dealt with is the ten months from August 1890 to May 1891. The whole of the hourly observations made at each Observatory with the barometer were reduced to sea-level, those at the top of the mountain being reduced according to the table accompanying the Report on the Meteorology of Ben Nevis.