from an inland region to the sea-coast makes us aware of what is commonly called the "odour of the sea," which was noticed as early as the days of Alexander the Great; for the old author, Quintus Curtius Rufus, distinctly informs us that the soldiers of Alexander knew when they approached the sea by the odour it diffused in the air-" agnoscere se auram maris."

Now, I have found that the fossil marine worms (Teredo), which I used often to obtain from the tertiary sands of Brussels, gave a distinct odour of the sea (aura maris), when broken with a hammer, or scratched with a knife, shortly after being taken from the strata in which they have been imbedded for myriads of centuries. This is infinitely more astonishing than the accounts of the extraordinary persistency of the odour of a grain of musk diffused through the atmosphere of a large room for a great number of years.

Travelling on foot in Germany, I was often able, during the night as well as by day, to distinguish when I was approaching a beech forest or a pine forest, by the different odour diffused through the air by each of these trees.

All these facts show that the lower regions of the air become impregnated with various volatile substances which are constantly produced on the Earth's surface, and the most minute quantities of which affect the delicate tissue of the sensitive olfactive nerves. I need

1 Phipson, "Note sur les Térédo fossiles," in the Comptes-rendus of the Paris Academy of Sciences, 1857.

not develop this subject further; but there is one observation I desire particularly to allude to, namely, the very delicious odour perceived in the air of a country garden after a heavy summer shower. For many years the cause of this odour escaped me completely until, one day in 1863, I found that certain specimens of chalk taken in the open country of Picardy, in France, developed a similar fragrance when they were dissolved in diluted hydrochloric acid. For a long time I was unable to trap the odoriferous substance which thus escaped with the carbonic acid; but finally I succeeded by passing the gas given off by the chalk through a solution of bromine in water. The bromine compound thus obtained was found to be analogous to bromo-cedren, showing that the odour was due to some essence like that of cedar. Hence, I was led to conclude that the pleasant fragrance diffused through the air in a country flower-garden after a heavy shower of rain, is due to the displacement by the rain of the flower-essences (essential oils) absorbed by the dry porous soil during the hot days of summer. Many years afterwards a well-known chemist in Paris made. some experiments, which fully confirmed my views in this respect (Chem. News, Lond. 1891).

So much has been written upon the peculiar state of oxygen known as ozone, that my remarks on this subject must be very brief.1 With us in England, I find it

1 Phipson, "La Force Catalytique," etc. (Soc. Holl. des Sc., Haarlem, 1858). See also the same author's papers in the Chemical News, London, from 1860 to the present time.

The bow what this gore is de sordid place a stick of

wens dufy w Test Tods Surving Frect from the Adactic and is ray peepahe i ging into the spent the being for some time in the close atmosphere of a moon for in de phosphorms in sice wher tomised in a large glass 2002, in sub a manner in about half the phosphorus mands above the whet In the acarse of a few hours the air of the glass globe will have a very strong odour of ozone, and will act upon a strip of paper steeped in starch with a linle iodide of potassium, turning it Lize

The presence of ozone in the atmosphere of any given Locality renders the air highly tenke, bracing, and antiseptic. It is rarely present in the atmosphere of densely populated districts, except when a westerly gale is blow. ing, as it is readily destroyed by the envia of animal life, and in presence of organic matter prone to oxidation, or in a state of decay. It is often present in sea-air. Some experiments which I published long ago (loc. cit.) have proved that whenever the atmosphere acts upon an organic substance, such for instance as a slice of apple, which it turns brown, the oxygen is immediately transformed into ozone (called by some "nascent oxygen," because when oxygen leaves a compound it is in the same state).

Again, ozone formed in an atmosphere at a very low temperature such as is met with in the Arctic regions, is liable to affect the flesh of animals exposed to it before being cooked, inducing all the effects of putre

ODOUR OF THE ATMOSPHERE.

47

faction, as was observed by the young and ardent explorer Dr. Kane in the famous Grinnell Expedition in search of Sir John Franklin.1

1 Phipson, "Sur la putréfaction à 35° sous zéro," in the Comptesrendus of the Paris Academy, 1859.

CHAPTER IX.

The Electric Phenomena of the Atmosphere-The Author's Researches and History of Electric Discoveries-Phosphorescence of the Air-Vibratory Nature of the Lightning-flash.

THE electric phenomena of the atmosphere have always been a source of the greatest interest, and the discovery of the nature of lightning by Benjamin Franklin was one of the greatest achievements of the last century. A history of Atmospheric Electricity is given in one of my former works,1 where I have traced the progress of this important branch of physical science from its birth to the present epoch, giving an account of Franklin's celebrated kite experiment and what led up to it. Long electric sparks had been obtained from the extremities of isolated metallic rods, raised high in the air, by Dalibard in France, some months before Franklin made his experiment; but it was at the suggestion of the latter. Such experiments are very dangerous, and the young Professor Richmann was killed in this way at St. Petersburg.

It is not necessary that storm-clouds should be present, for if an isolated condenser be suddenly 1 Familiar Letters on some Mysteries of Nature, London, 1876.