about three in the afternoon in winter. There is a second maximum at sunset, followed by a diminution during the night until sunrise. This fluctuation is connected with that of the hygrometric condition of the air. In the annual fluctuation the maximum comes in January, and the minimum in July; it is due to the great atmospherical circulation; the winter is the time when the equatorial currents are most active in our hemisphere, and when the aurora borealis is to be seen most often.

On the other hand, the water of oceans and rivers is continually evaporating under the influence of solar heat, and rises into the atmosphere, where it remains in the form of an invisible gaseous vapour. Soon it becomes cold again, and, in the process of condensation, transparent gaseous molecules become transformed into minute drops, which accumulate into a cloud.

Generally speaking, clouds are, like the atmosphere, charged with positive electricity. Sometimes, however, there are negative clouds. You may frequently see, on the summits of mountains, clouds which seem to cling to the peaks for a while, as though drawn to them by some force of attraction, and then move away to follow the general direction of the winds. It often happens that in this case the clouds have lost their positive electricity in thus coming in contact with the mountains, and have derived from them in its place the negative electricity which, instead of holding them, has a tendency to drive them off. A mass of clouds lying between the negative earth and a mass of positive clouds above is almost neutral; the positive electricity accumulates towards its lower surface, and the first drops of rain will make it disappear. This mass will, from that moment, become like the surface of the soil—that is to say, it will become negative under the influence of the mass above it, endowed with a strong positive tendency.

The cloud remains suspended in space until the moment when, under the influence of the ambient medium, it dissolves in rain.

The causes of the instability of clouds are very numerous. My readers are aware that the atmosphere is being constantly agitated by vast currents which pass from the equator to the poles, and from which the different winds result.

The clouds take part in this universal whirl of atmospheric waves. Transported from one point to another—often far beyond the region where they came into existence—subjected to every vicissitude of atmosphere, and blown about by contrary currents, they follow the gigantic movements which take the form sometimes of cyclones and tempests.

Under the influence of warmth, and probably also by its transformation, these movements engender great masses of electricity, and presently, when the clouds have become saturated with it, the electricity breaks out, and there is a thunderstorm.

The electric fluid, escaped from the cloud in which it has been imprisoned, flies to unite itself, either with the negative electricity stored in the surface of the earth, or else with the electricity in other neighbouring clouds. Almost always the cloud torn open by the electric discharge dissolves in rain or hail.

Thus a storm is the outcome of violent movements produced by the force of electricity when this has reached its maximum of intensity. Thunderstorms are generally heralded by certain premonitory signs. The barometer goes down steadily. The air, calm and heavy, is pervaded by a bitter sulphurous odour. The heat is stifling. An abnormal silence reigns over the land. All this has a remarkable effect upon certain organisms, and produces nervous complaints, a buzzing in the ears, a sense of painful oppression, a sort of good-for-nothingness that we combat in vain.

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 shining 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 masses of cotton-wool. These are termed cumuli. 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 space. The heavens, darkened over, seem to have sunk quite low, and to have become a great black mass, 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 masses, differently electrified—the lower one giving out negative electricity, the higher positive electricity. The flashes of lightning occur generally between these two masses, though also, less frequently, between the lower mass and the earth.

It may be said that, generally speaking, storms are the result of the meeting of two masses 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