176 
NATURE 
[Dec. 21, 1882 
of meteorology. Singularly enough, Great Britain alone 
stands aloof from participation in the general moveinent, 
and notwithstanding the heavy responsibility which her 
geographical position and vast pecuniary interests and 
resources impose upon her, none of the mountains that 
rear their heads in the very tracks of the storms which 
sweep over Europe from the Atlantic, is yet occupied by 
either observatory or station for systematic and continuous 
observation of the weather, the highest station in these 
islands being Dalnaspidal, which is only 1450 feet above 
the level of the sea. 
At high-level stations near the equator, where tempera- 
‘ture varies but little throughout the year, atmospheric 
pressure, which may be regarded as measuring the mass 
-of air overhead, is subject also to very small variation. 
‘Thus at Bogota, in South America, 8727 feet high, where 
the mean temperatures of January and July are respect- 
ively 57°°2 and 56°-2, the normal atmospheric pressure is 
22°048 inches and 22'058 inches. Let us look now at 
the results obtained at Pike’s Peak, where a first-class 
meteorological observatory was established by the United 
‘States Government about ten years ago, at a height of 
14,151 feet above the sea. Mr. Henry A. Hazen, in a 
recently published paper on “The Reduction of Air- 
pressures to Sea-level at Elevated Stations,’ shows that 
the normal pressure on Pike's Peak is 0°632 inch less in 
winter than in summer. The difference is mainly due to 
the low temperature of winter as compared with that of 
summer ; the reason being that the atmosphere in winter 
being condensed by the cold, sinks below the summit of 
the mountain, thus giving a lower pressure there. Now 
since a lowering of the temperature implies a proportion- 
ate condensation, or greater massing of the atmosphere 
in its lower strata, with a corresponding diminution of 
pressure in the upper regions, it necessarily follows that 
at considerable heights in the northern hemisphere the 
normal pressure is relatively higher in equatorial regions 
during the winter months, as compared with any other 
season of the year, than in higher latitudes at the same 
heights ; and that generally the diminution of the normal 
pressure in the upper regions is in proportion to the low- 
ness of the temperature of the lower strata. From this 
state of things it results that, during the colder months, 
the upper atmospheric currents flow northwards in greater 
volume, velocity, and persistency, bearing with them the 
higher temperature and humidity of lower latitudes. It is 
doubtless from the disturbing influences thus called into 
play, particularly the disturbing influence of the aqueous 
vapour from the Atlantic, that the notoriously stormy 
weather of the winters of North-Western Europe is to be 
traced. 
But the fluctuations of pressure at great heights in the 
atmosphere are not merely seasonal changes following 
the annual march of temperature through the year ; they 
also follow the changes of temperature which occur from 
day to day, notably those great and striking changes of 
temperature which accompany storms. Now it is the 
investigation of these changes, together with changes in 
the humidity, cloudiness, and motions of the atmosphere, 
in their relations to the cyclones and anticyclones of 
Europe, with the stormy and settled weather that respec- 
tively accompanies them, which give to meteorological 
observations made on Ben Nevis their international 
significance. 
The observations made during the summer of 1881 on 
the top of Ben Nevis, in connection with the Scottish | 
Meteorological Society, by Mr. Wragge, with an en- , 
thusiasm, physical endurance, and undaunted devotion to 
the work beyond all praise, have now been to some extent | 
discussed, with the result that they amply bear out the 
strong opinion here advanced of their great value in fore- 
casting weather. The time was sufficiently extended for 
the determination of the approximate normal differences 
between observations at the top of the Ben and at Fort | 
William, near sea-level. During the unsettled weather 
of the summer of 1881, departures from the normal values, 
and these departures often large, were of frequent occur- 
rence. Now the remarkable and frequent differences 
from the normals thereby disclosed in the vertical distri- 
bution of atmospheric temperature, humidity, and pres- 
sure in the aérial stratum between the top of Ben Nevis 
and sea-level, taken in connection with the weather that 
followed, give the strongest grounds for the assurance that 
observations made on the top of Ben Nevis would con- 
tribute invaluable aid, if directly wired to London, in 
framing forecasts of weather for the British Islands and 
North-West Europe generally. The observations also 
threw no little light on several controverted points 
respecting the movements of cirrus clouds, upper currents, 
and the time when the centres of storms reach higher and 
lower levels respectively. 
The observations were resumed last summer on a more 
extended scale, the new observations embracing a more 
complete investigation into the varying states of the 
atmospheric stratum between the top of the mountain and 
the sea, by a string of intermediate stations at different 
heights, and by a very elaborate and carefully worked 
out system of ozone observations. The weather of 1882 
differed materially from that of 1881, and when the ob- 
servations of 1882 come to be discussed, they will doubt- 
less yield new results in the further extension of our 
knowledge of weather phenomena. Among the new 
results may be mentioned the remarkable observations 
with the hygrometer in the second week of August and 
at the equinox. The most striking of these were the ob- 
servations of September 21, when the dry and wet bulbs 
on the top of the mountain read as follows :— 
Dry Wet Dry Wet 
Qu aim) Snag Eats ora: 10°30 a.m. ... 51°9 ... 390 
9°30 5, + 49°5 --. 39°7 | IT 99. Chat SI nes 7EO 
10 ” ++ 494 --. 37°99; 11°30 5, v 53°77 + 404 
the barometer at Fort William being high at the time 
and nearly steady. No such relatively warm and dry air 
was recorded at Fort William where during the time the 
temperature was only from 1°9 to 4°°6 higher than that 
of Ben Nevis, instead of the normal difference 15°°7. It 
is instructive to note that these hygrometric states of the 
atmosphere were odserved on the top of Ben Nevis, 
during, or more strictly speaking, towards the termina- 
tion of a rather protracted and heavy storm from the 
north, which 1olled huge breakers on the beach of the 
Moray Firth, and poured down deluges of rain on the 
high northern slopes of the mountain range stretching 
from near Foyers to Huntly, which flooded the rivers to 
an unusual height. The unwonted warmth and dryness 
of the air, and the deluges of rain that fell immediately 
to the northward, warrant us in classing the singular 
phenomena recorded by Mr. Wraggeon the top of Ben 
Nevis on the morning of September 21, as quite analo- 
gous to the fohn of Switzerland. If the supposition be a 
correct one, the difference between the two classes of 
phenomena is, that whilst the fohn of Switzerland has its 
origin in a saturated atmosphere discharging its super- 
abundant vapour in deluges of rain on the southern 
slopes of the Alps, and after crossing these moun- 
tains, descending the northern steeps of the mountain- 
range as a dry warm wind, the fohn of Ben Nevis 
had its origin in the highly saturated air, which, ad- 
vancing from the North Sea, discharged its vapour on 
the higher slopes looking down on the Moray Firth, and 
after ascending to some height, thereafter blew down on 
Ben Nevis as a descending wind, characterised by a dry- 
ness and relative warmth rarely felt at lower levels. The 
value of these observations from their important bearings 
on the theory of storms and other atmospheric move- 
ments, cannot easily be over-estimated by the meteoro- 
logist, and it is important to note that the observations 
