METEOROLOGICAL OBSERVATIONS ON BEN NEVIS. WA 
and December, which were substantially occasioned by the very low tem- 
perature of these months, so that the high-level pressure, when reduced 
‘to sea level, closely agrees with the sea level pressure at Fort William. 
In September, however, though the mean temperature was 3°°5 and 
5°-4 respectively above the averages, the difference between the mean 
pressure at the two Observatories was 4487 inches, the September averages 
of the previous 15 years being 4:450 inches. The characteristic of the 
weather of the month was eminently anticyclonic, and as the anticyclones 
extended, in a modified form, downward, considerably below the level of 
the summit, they carried down with them their characteristically very dry 
and therefore heavier air, thus increasing the density of the aérial stratum 
between the top and bottom of the mountain, above what would have 
been if this stratum had been of the usual humidity. Hence pressure at 
Fort William was relatively higher, and consequently the difference 
between pressure at the top and bottom was correspondingly increased. 
But during the last three days of the month over Scotland the sky 
was clear, sunshine strong, humidity high, night temperatures unusually 
high, and dews heavy, with calms or light winds. The weather of this period 
has been discussed with some fulness in a paper published in the last 
issued ‘ Journal of the Scottish Meteorological Society,’ to which reference 
may be here made. On these days, while at the top temperature was 
very high and the air clear and very dry, at Fort William, under a sky 
equally clear and temperature high, the air showed a large humidity, and 
this state of moisture extended to a height of about 2,000 feet, or nearly 
halfway to the summit. Thus, then, while the barometer at the top was 
under an atmosphere wholly anticyclonic, with its accompanying dry 
dense air, the barometer at Fort William was not so circumstanced. On 
the other hand, it was under the pressure of such dry dense air, above 
the height of 2,000 feet only, whereas from this height down to sea level 
it was under the pressure of air whose humidity was large and pressure 
therefore much reduced. The result was that the sea-level pressure at 
Fort William was 0-050 inch lower than it would have been if the dry 
dense air of the anticyclone had been continued down to Fort William. 
This is confirmatory of what is to be expected, that the greater density 
of dry air as shown in our laboratories prevails equally in the free 
atmosphere. 
The discussion of the observations reveals numerous instances of an 
opposite condition of things, viz., the air at the lower levels remaining 
comparatively dry, while aloft at higher altitudes it is becoming rapidly 
moister, the moister air gradually occupying lower levels as a cyclone is 
advancing. In these cases the lower barometer reads—not the relatively 
ower, but the relatively higher, of the two. An important result is 
emerging as the discussion proceeds, since it appears that an indication 
is hereby given towards a more accurate knowledge than is at present 
possessed of the intensity of a coming cyclone and of the attendant anti- 
cyclone. 
: In addition to the variability of the distribution with height of the 
humidity, the distribution of the temperature is also being particularly 
investigated, especially as regards the light it casts on the interpretation 
of the causes leading to the variability in the vertical distribution of the 
pressure. This department of the inquiry is in the hands of Mr. Omond, 
who read a preliminary paper on the subject at the meeting of the 
Scottish Meteorological Society in July last. 
