1892-93.] A. J. Herbertson on Atmosphere at Ben Nevis. 177 
Preliminary Note on the Hygrometric State of the Atmo- 
sphere at Ben Nevis Obsqrvatory. By Andrew J. 
Herbertson. Communicated hy Dr A. Buchan. 
(Read February 6, 1893.) 
The present communication consists of a description of the 
apparatus and methods employed in a series of hygrometric experi- 
ments recently made at the Ben Nevis High-Level Observatory, 
and a very brief notice of some of the results obtained. The 
investigation here outlined is a necessary preliminary to a more 
elaborate one, which, it is hoped, may be carried out this summer. 
The gravimetric method of estimating the quantity of water vapour 
in a known volume of air was adopted, and readings of dry and wet 
bulb thermometers were taken during the experiment. 
The apparatus was fitted up at the Low-Level Observatory in Fort- 
William at the beginning of September 1892, and found to be in 
working order. It was then transported to the summit station, 
and used whenever possible until a month ago. Experiments were 
made in hygrometric conditions varying from saturation to that 
extreme dryness which is occasionally experienced on Ben Nevis. 
Apparatus . — A 6-inch U-tube, with a small bulb blown at the 
bend and an L piece of narrower tubing fused to one arm, was filled 
Fig. 1. 
with granulated pumice, which had been washed with sulphuric acid 
and then heated until fumes ceased to be given off. A second piece 
VOL. XX. 23/3/94 M 
