Part 2 (1/2)

In most cases storms come to us in France ready made, so to speak, from the sea, borne in by the currents from the south-west; they are the off-shoots of the cyclones, and are born in the tropics, moving in lines from the south-west to the north-east. Ordinarily they lose part of their strength _en route_ and come to an end suddenly with us.

There are, of course, home-made storms also, so to speak, especially in France during our hot summers, when the sun is s.h.i.+ning all the day, and thus promoting the rapid evaporation of our seas and rivers.

The air is charged with a heavy mist which veils the horizon; the barometer is going down, the thermometer going up. The sun looks leaden though there are no clouds. When it approaches the meridian and its rays are most scorching, columns of vapour ascend and become condensed into the light clouds termed _cirri_. At the end of some hours these clouds become attracted to each other, descend a little, and become grouped together into what look like great ma.s.ses of cotton-wool. These are termed _c.u.muli_. Presently a small grey cloud joins the others. It looks innocent and harmless, but very often this is the beginning of the battle. First there ensues, perhaps, a discharge or two of lightning without casualties, but soon the bombardment becomes general, and long blinding fusillades flash through s.p.a.ce. The heavens, darkened over, seem to have sunk quite low, and to have become a great black ma.s.s, from which the lightning escapes in sudden jets. Rain and hail pelt down upon the earth to an accompaniment of the rumbling of thunder. Confusion has fallen upon the entire universe.

Then, finally, the fight comes to a close. The clouds disperse and allow us to see once again a wide expanse of sunlit blue. The birds, their hearts freed again from terror, begin to sing again. Flowers and foliage and soil, refreshed by the rain, give out sweet perfumes. An immense joy takes the place of the sense of melancholy and oppression.

It is good to see the sun again! Alas, though, there are grim realities to be faced presently. The hailstones have destroyed the crops and begotten famine--the lightning has sown death and plunged whole families into mourning. It is with these misfortunes before us that we make up our minds to do what in us lies to diminish the destructiveness of this terrible force.

How are storm-clouds to be detected?

Generally speaking, their shape is very clearly defined, and they have a look of solidity about them.

Their lower surface is often unbroken, presenting a level plain from which there rise huge ragged protuberances like great plumes.

Sometimes, on the other hand, they have great projections underneath, trailing quite near the ground.

Storm-clouds move generally in large numbers, and are generally composed of two separate ma.s.ses, differently electrified--the lower one giving out negative electricity, the higher positive electricity.

The flashes of lightning occur generally between these two ma.s.ses, though also, less frequently, between the lower ma.s.s and the earth.

It may be said that, generally speaking, storms are the result of the meeting of two ma.s.ses of clouds differently electrified.

For long, physicists refused to admit the validity of any other theory, and combated in particular the idea that lightning could issue from a single isolated cloud.

This has, however, been established now as a fact, and in such cases the flashes have always, of course, taken place between the cloud and the earth.

Marcorelle, of Toulouse, reports that on September 12, 1747, the sky being then pure and cloudless but for one round speck, there was suddenly a thunderclap and a flash which killed a woman on the spot, burning her breast but doing no damage to her clothes.

Here is another interesting case. Two priests of the Cathedral of Lombey, who were standing in the area of their chapter-house, busy winnowing, saw a small cloud approaching them little by little. When it was immediately above them a flash of lightning broke out and struck a tree just beside them, splitting it from top to bottom. They heard no thunderclap. The weather was quite fine. There was no wind, and this was the only cloud in the sky.

Storms are far more prevalent in some countries than in others.

According to Pliny, thunder was unknown in Egypt, and, according to Plutarch, in Abyssinia. This could not be said now, however, perhaps because these lands have grown unworthy of their exemption. It might be said, however, of Peru, whose pure and limpid skies are never troubled by tempest. _Jupiter tonans_ must be a myth indeed to a people who know nothing of thunderclaps or wet days.

Storms diminish in number in high lat.i.tudes, but there are local conditions which affect their distribution. Then they are particularly frequent in countries that are thickly wooded and in mountainous districts.

Arago came to the conclusion, after a considerable number of observations, that, out in the open sea or among islands, there is no thunder in the north beyond the 75th degree of lat.i.tude. This is not absolutely so, but it is a fact that storms are very much rarer in the polar regions. They become more and more frequent towards the equator, and are very numerous in the tropics.

On either side of the equator storms come year after year with remarkable regularity in the wet season, and at the time of the monsoons.

At Guadeloupe and Martinique there is never any thunder in December, January, February, or March.

In temperate climates there are scarcely any storms in winter; they begin in the spring, and attain their maximum of intensity in the heat of summer.

In Italy there are thunderstorms at almost all times of the year.

In Greece they come chiefly in spring and autumn.

It is noticeable that in all lat.i.tudes they come most often in the afternoon.