Beccher, and his follower Stahl, came next with a singular theory (phlogiston) that threw men's minds, for a time, out of the correct line; and, strange to say, this phlogistic theory was kept up by Priestley, whose experiments on air, with those of Schéele and Lavoisier, finally led to the foundation of modern Chemistry.

I cannot in this work devote space to the purely chemical investigations which gradually led us to a knowledge of the various gases which compose the Atmosphere. They must be sought for in treatises on the history of Chemistry and Physics. I can only say that, like all great discoveries, this knowledge was derived from the labours of a large number of ingenious men, among whom the most conspicuous are Van Helmont (of Brussels), Jean Rey, Bayen, Hooke, Mayow, Hales, Stahl, etc. To Priestley, Schéele, and Lavoisier is due the discovery of oxygen; Black (of Glasgow) discovered the nature of carbonic acid. Nitrogen was actually discovered in 1772 by Dr. Rutherford, then Professor of Botany in Edinburgh (De Aere mephitico). Oxygen was discovered about the same time by Priestley, Schéele, and Lavoisier. In 1773 the latter gave us the first analysis of the air (finding 27 to 28 per cent. of oxygen, instead of 21). He began his researches in

the flame of a candle" (Clavis philosophorum in Theatrum chemicum, iv. 1141, and Hoefer, Hist. de la Chimie, i. 471).

In very ancient times Hippocrates recognized in air his "pabulum vita" (oxygen), and Democritus knew that it contained a vital principle which fixed itself in the body during the act of breathing. (See Aristotle, De Respiratione.)

1770, and finally announced in 1774 that "in every case of combustion oxygen combines with the burning body," and from that moment the Science of Chemistry was revolutionized, or, rather, created. Yet years elapsed before he could make a single convert to his views!

The labours of Cavendish on hydrogen (1774), and the speculations of James Watt and others, led to the knowledge of the composition of water. "Ozone," or allotropic oxygen, was discovered by Schoenbein of Basle in 1845, and "argon" (or "allotropic nitrogen"?) by Rayleigh and Ramsay in 1894.

The ancients, with Aristotle, considered air to be one of the "four elements": fire, earth, air, and water. It was also believed to have no weight.

In the early part of the seventeenth century an obscure apothecary named Brun, living in the little town of Bergerac, in France, noticed that when tin was melted over a hot fire, it formed a kind of earth (or, as we should now say, an oxide), and gained in weight. He asked a medical man of his acquaintance, Dr. Jean Rey, who practised at the neighbouring village of Bugue, in Périgord, how he would explain this, and the doctor repeated the experiment several times. Finally, in 1630, he published a now celebrated pamphlet on the question, in which he declared that tin, when heated, absorbed air and increased in weight. This was a remarkable conclusion to arrive at, for in those days air was supposed to have no weight.

More than a century later, when this pamphlet by Jean Rey was quite forgotten, another French observer,

named Bayen, found that the same curious phenomenon occurred with mercury, and he concluded that all metals increased in weight when they were calcined. Finally, the celebrated Lavoisier repeated this experiment with mercury, and found that metals only absorb a portion of the air, that portion now known as oxygen gas. He thus made the first analysis of atmospheric air, as I have already stated.1

The weight of the air was discovered in the following singular manner by the illustrious Galileo in 1640, and his opinion was soon confirmed by Torricelli (his pupil) and by the French philosopher Pascal.

Galileo carefully weighed a large vessel full of ordinary air, and then the same vessel full of compressed air. A difference of weight was noticed, and this showed that the air was a body possessed of weight. Not long afterwards, some well-sinkers at Florence endeavoured to get water to rise more than 32 feet in a pump, and failing to do so, they asked Galileo the cause of this failure. In those days the rising of water in a pump was said to be due to the fact that "nature

1 Nevertheless, it has now been ascertained that this experiment is much older than has hitherto been supposed. It has been discovered that Eck von Sulzbach, a man usually confounded with the German alchemists of the latter part of the fifteenth century, was really the first to notice that metals increase in weight when calcined. His experiment was made with mercury, and with an amalgam of silver, and he distinctly states that this increase in the weight of the metal after calcination is due "to a spirit which fixes itself to the body of the metal," and he also says that when the latter "is distilled, this spirit is set free." Eck von Sulzbach made his second experiment in 1489, so that these facts had been ascertained nearly three hundred years before Lavoisier's experiment. (Compare Dr. F. Hoefer, Hist. de la Chimie.)

abhors a vacuum"; and to explain the failure just alluded to, Galileo is reported to have replied: "Yes, nature abhors a vacuum, up to 32 feet, but not beyond."

This little incident set his pupil, Torricelli, thinking over the problem. He imagined the rising of the water in the pump was due to pressure (or weight) of the air, and that this pressure was only equal to a column of 32 feet of water. He took a long tube of glass, filled it with another liquid, mercury, turned it upside down, and allowed its open end to rest on a bath of that metal. He saw that the column of mercury stood at a height of about 13 times less than that of the column of water in the tube of the pump, and as mercury is about 13 times heavier than water, it was evident that the same cause acted in both instances, and that cause was the weight (or pressure) of the air.

Such being the case, the mercury in the glass tube should stand lower on the summit of a high mountain than in the valley, since it would have a less weight of air over it. This was proved to be so, by Pascal and Perrier, and so the barometer became at last one of the most useful of physical instruments in the hands of the meteorologist, the chemist, the physician, the sailor, the farmer, and the engineer.

In bringing forward these modest contributions to so vast a field of research and observation, I must solicit a large amount of indulgence on the part of my readers. It is not my desire simply to reproduce here what is to be found in standard works on Meteorology, but to give, as well as I can, the results of my own personal obser

vations with as many new facts as possible, whilst I rely, for the rest, on the useful and interesting nature of the facts recorded.

I trust that my little work will thus help to diffuse more exact knowledge with regard to the nature and properties of atmospheric air, and so contribute to promote, in many ways, the welfare of mankind.

The atmosphere, as we know it at the present day, forms over the surface of the globe a vast layer of invisible gas, extending to a great height, and charged with emanations of all kinds, but chiefly of aqueous vapour. When we subtract from it this aqueous vapour, and a minute amount of carbonic acid, it is found, in all parts of the world, to consist of a mixture of two gases, nitrogen and oxygen, in the proportion of 79 of the former to 21 of the latter.1

1 The new gas called "Argon" recently discovered in small quantity in the air by Lord Rayleigh and Prof. Ramsay, to which I make reference in another part of this little work, appeared to be a peculiar form of nitrogen, similar to what ozone is as regards oxygen. I was the first to call attention to this circumstance in a note inserted in the Chemical News (1894), and my opinion has been since confirmed by Prof. Berthelot of Paris (Comptes-rendus, March 1895). Prof. Dewar seemed to be of the same opinion. It might also be a compound of carbon and nitrogen, containing half as much carbon as cyanogen; such a compound would have the same specific gravity. But it is impossible at the present time to speculate upon the real nature of this new substance, as so very little is known about it. One hundred volumes of atmospheric air contain less than one volume of " argon," and its name is due to its inert nature, its negative properties being apparently greater than those of nitrogen itself. But whatever may be its real nature, argon is only present to such an insignificant amount (barely 1 per cent.) that it can exert no influence upon the general properties of the air, nor, considering its inert character, upon animal or vegetable life.