temperature in our climate, for every day of the year for forty years, I find that, in any given month of the year, this line tends to rise in a very marked manner from the 10th to the 25th of each month. The only remarkable exception to this law is during the few cold days about the 12th May, which, as I have previously hinted, are probably due to the absorption of atmospheric heat by the melting of the winter snows and icebergs, and to the position of the belt of November meteors, which, at that period, is between us and the sun.

CHAPTER XX.

Aërolites, or Stones from the Air-"Thunderbolts". -A Stroke of Lightning-A Fall of Meteoric Stones-Belt of Meteorites round the Earth Shooting-star Orbits and Comets Old Opinion of the Indefinite Extension of the Earth's Atmosphere.

THERE was a time, not so far distant from us, when aërolites stones from the air-were supposed to be formed in the atmosphere of the Earth, from the exhalations of the soil becoming condensed in the higher regions, and then falling heavily to the ground.

The phenomena which accompany these falls of aërolites, of which one, at least, occurs every year upon some part of the Earth's surface, are so similar to what is observed when lightning strikes any object, that they were once called "thunderbolts"; and as aërolites always contain more or less sulphur, the common rolled pyrites (sulphide of iron), found on the sea-shore, also got this appellation of "thunderbolts," and these rounded stones of common mundic, were often put away in collections as "aërolites," or "meteorites"—that is, stones which have fallen from the sky.

When lightning strikes an object on the Earth's

surface (as it did on the 17th April 1895, at about 4 p.m., between Putney and Barnes, a few yards from where I stood), the effect is like that of a large piece of artillery. The light and sound are instantaneous; a ball of vivid red light, about the size of a child's head, shoots from the sky to the earth with greater rapidity than a ball from the mouth of a gun, and the single report of the explosion is coincident with the flash.

In the case of a fall of aërolites, the noise occurs like a rumbling of loud thunder, which is heard only some considerable time after the fall of the stones. There is also a peculiar metallic ring in the thunder of the aerolite; but I have heard that, also, when lightning strikes, as it did in July 1894, a short distance from where it fell on the 17th April 1895, as just mentioned. It is like the shaking of huge chains. I have heard it on some other occasions also; so that the metallic sound may occur in both cases.

The lightning stroke leaves nothing behind it save a slight mist, an odour of sulphurous vapour, and its peculiar effects on trees, animals, or houses, etc. In many cases, houses have been struck by lightning, and the inmates have experienced nothing but alarm from the noise, little or no traces of any effects being afterwards found. After a fall of aerolites the stones are found either on the ground or buried a few feet below the surface.

In my volume on Meteors, Aerolites, and Falling Stars, published in 1867, I have given a complete history of these phenomena, and their distinctive character

istics. I have there given the chemical composition of all the principal aërolites which have been picked up shortly after they were seen to fall, and then submitted to analysis; also, a classification of the three kinds. according to the amount of metallic iron they contain.

This amount may vary from less than 1 per cent., to 98 or 99 per cent., the rest consisting of silicates and sulphides, but it is always present, and it always contains some nickel (another magnetic metal, like iron).

In the work just mentioned, I have also given a theory of my own with regard to the origin of aërolites, namely, that they form a ring of minute satellites around the Earth, like the ring of Saturn-which is now, also, being found to consist of a vast number of minute satellites, and so far confirms my theory of 1867.

At certain intervals, the position of the Earth in its orbit is such with regard to other planetary bodies, that some fragments from this dark ring are attracted to its surface, and crash through the atmosphere as "fire-ball meteors," which explode with violence, and shower down. stones, or metallic fragments of various sizes-from that of a walnut or less, to that of a man's head; or, even, far greater than this, if the immense masses of iron found in Australia (now in the British Museum), and at Ovifak, Greenland, are really aerolites.

These falls of stones from the atmosphere have been observed for some hundreds of years before Christ, down to the present time. Formerly, they were

thought to be shot from volcanoes in the Moon. They are, no doubt, of the same chemical composition as the Moon; and are, I believe, minute satellites of our Earth, thrown off like our larger satellite was thrown off, in the earliest ages of its existence.

That is, perhaps, a better theory than supposing them to be shot out from our terrestrial volcanoes in activity at the present time.

Shooting-stars are quite different.

Formerly, they

were thought to be the same phenomenon as bolides, or aërolites and I myself classed them all in one category, which a learned writer in the Saturday Review thought rather premature and he was right. Since the discovery made by the Italian astronomer, Schiaparelli (made known since my work on Meteors was published), that the swarms of shooting-stars which arrive in our atmosphere at certain stated intervals, present the same orbits as comets, these two classes of natural phenomena (comets and shooting-stars) are believed to be one and the same. Before Schiaparelli's time, Reichenbach

held a similar opinion.

This is what I wrote on aërolites in 1867: " Taking especially into consideration the chemical composition of aërolites, we may be tempted to suppose that these meteoroids have orbits round the Earth, not round the sun, and that they constitute a series of dark rings around our globe, similar, perhaps, to the rings of Saturn." (Meteors, etc., loc. cit.)

This quotation is interesting now that Professor Keeler, and others, are endeavouring to prove that