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able manner: the absence of some of the spectral lines of oxygen, when the Sun is viewed from the summit of Mont Blanc, has recently led the well-known French astronomer, M. Janssen, to the conclusion that there is probably no oxygen in the Sun's atmosphere.
My friend, Piazzi-Smyth, when Astronomer-Royal for Scotland, was the first, many years ago, to carry an astronomical telescope into the higher regions of the atmosphere. With the view of avoiding the influence of a dense layer of air, he took his instrument to the top of the Peak of Teneriffe, where he made some very interesting physical and astronomical observations. These were, on his return to England, the occasion of the publication of one of the most curious and delightful books in our language (An Astronomer's Experiment, etc.).
Since then, we have had a number of similar observations by Professor S. P. Langley, of Washington, which have been carried out on the heights of the Californian mountains, in one of the districts of the globe where the atmosphere is extremely pure, and where he was provided with one of the finest telescopes ever constructed. Under these most advantageous circumstances, Mr. Langley made observations on the heat and colour of the sun and planets, the distribution of the lines of the spectrum, the constitution of the solar surface, the distribution of light and heat upon the disc, the extent of the absorbing power of the Sun's atmosphere, and that of our Earth, the temperature of the Sun (which he fixes at some degrees higher than
the fusion point of platinum), and many other important researches, to which we need not here refer.
I should mention, also, the recent curious experiments made by Professor Dewar, of the Royal Institution, on the liquefaction of oxygen gas and of atmospheric air, accomplished by the application of intense cold and pressure. In following up the experiments of Pictet and others in this direction, our English professor has gone a step further (Chemical News, 19th January 1894), and his results have excited general interest. Berzélius recognized that the true colour of atmospheric air is blue, and the liquefied oxygen of Professor Dewar is likewise blue. It possesses the most singular properties, being without any action upon such inflammable metals as potassium and sodium, which shows what an enormous influence is exerted by temperature on chemical action. This became evident, years ago, in experiments by the celebrated Faraday1 as regards liquefied gases. He found that liquefied protoxide of nitrogen would not act on potassium, nor liquefied chlorine on antimony, etc.
1 See Dumas, Éloge de Faraday, p. 12.
Sulphur always present in the Atmosphere-Characin, the Cause of the Odour of Marshy Air-Odours of the Air in Different Countries-The Odour of the Sea-Air-Detected by the Author in Marine Fossils of the Tertiary Period-Odour of the Air after a Summer Shower--Observations regarding Ozone.
PURE air is odourless and tasteless, except when ozone is strongly developed, or when lightning strikes an object on the surface of the Earth. In the latter case, an odour of sulphurous acid is distinctly noticed, as I have had occasion to observe more than once. On one
of these occasions, in Paris in 1858, it affected the neighbourhood for a considerable distance around, and penetrated all the houses.
This odour of sulphurous acid is likewise perceived at sea when a ship is struck by lightning. It proves the existence of a certain amount of sulphur, or some compound of sulphur, in the air, even hundreds of miles. from land.
That sulphur, in some form, is a constant constituent of the Earth's atmosphere appears to be becoming less doubtful every day. In the early part of this century a writer in the Archiven der Pharmacie, named Dulk,
reported that after a storm of thunder and lightning which broke over Osterrode, in Prussia, on the 22nd April 1836, a yellow powder was found in the water collected from two streams. It was formed of coarse grains, like small hailstones, some of which were nearly as large as peas, and these formed semi-transparent drops, which were fragile, and could be easily broken between the fingers. Afterwards, the grains became a darker yellow, and harder; so that they could no longer be broken by pressure between the fingers. It was proved that these yellow grains were sulphur, much purer than the ordinary brimstone of trade. Mr. Dulk, and his friend Mr. Lange, then requested the Mayor of Osterrode to enquire of the proprietors of the streams what had happened. The latter, and their servants, all declared that there had been no sulphur before the storm, and that after the storm, sulphur had not only been found in the two streams, but in the gutters, and empty vessels, such as saucepans and tubs, belonging to artisans in the neighbourhood.
The so-called "sulphur rain" due to the pollen of the Pine trees, often observed in Norway and Sweden, has been occasionally witnessed also at Oleron in the Basses Pyrénées (France).
Another cause of odour in the air, extending over wide districts of marshy lands, is due to the volatile substance characin, which I discovered in 1879.1 It forms very thin iridescent films on the surface of stagnant waters where algæ abound, and on the water of
1 Chemical News, London, 1879.
tanks in which these microscopic plants are cultivated. It is soluble in alcohol and ether, and is volatile, it possesses the characteristic odour of marshy air, so intense during hot summer weather in the flat districts of Flanders, especially along the wide ditches which border the Chaussées, where I first noticed it. It has the odour of the Chara, hence the name I gave it, and to most persons is very disagreeable (botanists call one of the species Chara fœtida); but all fresh water Algo produce it, Conferva, Palmella, Oscillaria, etc.; and it is often to be noticed, during hot weather, in glass tumblers which have been wiped out with a towel on which microscopic Algo have developed, through want of cleanliness, and neglect of soaking the glass-towels in boiling water. Characin may, of course, be produced by the influence of microbes, but it is quite distinct from them, being a well-defined substance, approaching to the nature of camphor.
I have noticed, during my travels in Europe, that on passing from one country to another, a different odour is perceptible in the atmosphere. If we take the boat to Ostend, for instance, we are at once struck, on arriving, by the peculiar odour in the air; and the traveller who proceeds from Belgium to France, from France to Germany, etc., can scarcely fail to notice the peculiar change in the odour of the air when he changes his abode to reside in another country. The cause of this must be looked for in the various modes of life of the inhabitants, and has little to do with the natural constituents of the atmosphere. But even a journey