The Ben Nevis Observatory

24 Oct

I have always been interested in the history of the Ben Nevis Observatory. I have written about it before but I think this remarkable development deserves further comment.
The observatory was opened on the summit of Ben Nevis (4,406 feet), in October 1893; and enlarged in 1894, but observations (as distinct to the actual Observatory) started in 1881, when a determined meteorologist Clement Wragge climbed Ben Nevis to make recordings. He got to the summit virtually every day between early June and mid October and used pigeons to transport his readings to Fort William where his wife took the low level readings and telegraphed the results to London! Wragge hoped that after his considerable efforts, he would be the first Supervisor when the observatory was built, but he was passed over in favour of the experienced meteorologist, Robert Omond.
William Speirs Bruce applied to join the Observatory in1894, he needed experience in recording detailed meteorological data in relation to his plans to lead an expedition to Antarctica. Initially his appointment was a locum post, but he was appointed to a substantive position on the summit, under the leadership of Robert Omond, in1895. His aim to achieve meteorological experience was achieved; in his year on the summit was given the most rigorous training.
In 1896 a Low Level Observatory was built at Fort William and manned by Robert Mossman, who would become closely associated with Bruce and went on the Scotia expedition as Meteorologist. The recordings from these two levels were synchronised, this was a first in Britain and led to increased understanding of weather conditions in mountainous regions.
Bruce’s duties were onerous. Observations were made, every hour whenever possible, in rapidly changing and often challenging, conditions. In winter, when snow made the station isolated enough even for Bruce, the snowdrifts were sometimes so high that the men had to get to their instruments via snow tunnels, or exit the observatory via the tower. This experience plus the changes in wind and fog, was an excellent training for Antarctic meteorology.
It was found that fog was present on the summit for 80% of the time in November, December and January 1895/6 – it was common for the summit to be capped in fog when surrounding summits were clear (later Bruce was to tell his companions in Antarctica that they did not know what fog was unless they had experienced it on Ben Nevis). Temperature comparisons between the high and low stations showed that the average fall in temperature between Fort William and the Summit was 15.3°F, with a mean annual temperature at the summit of 31.5° F, compared with 46.8°F. at the base station. Annual rainfall at the summit was approximately double that at Fort William.
Distinguished scientists visited the summit to observe its activities. Amongst these was C.T.R.Wilson, a Scottish physicist. One morning Wilson noted that the rays of the sun cast his shadow, enormously magnified and surmounted by a coloured halo, onto the surface of a fog cloud on the opposite mountain top (this phenomenon had been described by Johann Silberschlag in 1780 and was called the Brocken Spectre).
Wilson recognised that this phenomenon was due to supersaturated water droplets, in the form of fog, which fragmented the sun’s rays into its component parts.
In subsequent laboratory experiments he used sealed glass containers of supersaturated water droplets, (which he called the Cloud Chamber), to demonstrate images of the tracks of charged particles released by X-rays and radioactive materials. Different sized particles with different speeds created different trail patterns – for example an alpha particle track is thick and straight, others are wispy.
The Cloud Chamber was the first tool to be able to follow the path of otherwise invisible particles and show the variety of their size and speed. Wilson was awarded the Nobel Prize in 1927 for this work.
Bruce spent a year on Ben Nevis. Sadly recurring shortfalls in funds led to the observatory being closed in 1904, nine years after he had left it.

The cloud chamber is described as follows: a sealed environment containing a supersaturated vapour of water or alcohol. An energetic charged particle (for example, an alpha or beta particle) interacts with the gaseous mixture by knocking electrons off gas molecules via electrostatic forces during collisions, resulting in a trail of ionised gas particles. The resulting ions act as condensation centres, around which a mist-like trail of small droplets form if the gas mixture is at the point of condensation. These droplets are visible as a “cloud” track that persist for several seconds while the droplets fall through the vapour. These tracks have characteristic shapes. For example, an alpha particle track is thick and straight, while an electron track is wispy and shows more evidence of deflections by collisions.
Cloud chambers played a prominent role in the experimental particle physics from the 1920s to the 1950s, until the advent of the bubble chamber. In particular, the discoveries of the positron in 1932 and the muon in 1936, both by Carl Anderson (awarded a Nobel Prize in Physics in 1936), used cloud chambers. Discovery of the kaon by George Rochester and Clifford Charles Butler in 1947, also was made using a cloud chamber as the detector. In each case, cosmic rays were the source of ionising radiation.

caption: Ben Nevis Observatory after Ice storm
(photo facing page 64 N.Rudmose Brown’s’Naturalist at the Poles’)

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