We have already spoken of rain, hail, and snow; it is time to discuss the great agent of storms - Electricity, which exists latent probably in nearly all terrestrial objects, and is seen in nature as lightning.

There are two kinds of electricity - Vitreous and Resinous; called by Dr. Franklin the Positive and Negative. Vitreous electricity is so called because it was first produced by rubbing glass: Resinous, because it was best procured by rubbing resinous substances.

Electricity accumulates in the clouds from different sources: from evaporation from the earth's surface; from chemical changes in the air; and from friction between currents of air of unequal temperature crossing each other. Lightning is this accumulated electricity discharged from the' clouds, by one kind of electricity rushing from a cloud to unite itself with the other kind, in another cloud, or in the earth. The flash parts the; atmosphere, and the concussion made when the air closes again, produces (in great part) the noise which we call thunder. When the lightning-cloud is near the earth all the vibrations of the air (on which sound depends) reach the ear at the same moment, and produce one terrific crash. When the lightning cloud is a long way off, and some of the vibrations of sound have further to travel than others, the peal reaches the ear at intervals and is broken and irregular. The vibrations produced in the lowest portions of the air are heard first. The flash is instantaneous, but sound takes a second of time to travel 380 yards.

The lightning clouds are often very near the earth. They are rarely more than 700 yards from the surface when discharged, and the nearer they are the more likely they are to discharge. Any high object which, reduces the distance between them and the earth, as steeples, high trees,, etc., will discharge them.

Electricity passes through a conductor in a quiet and invisible form; when it cuts the air it becomes visible, because the atmosphere is a bad conductor.

Example of the zigzag path of Lightning.

Lightning is forked when the flash is divided by terrestrial objects which attract it; it is zigzag when it condenses the air in its immediate path, and flies from side to side that it may pass where there is least resistance. When the distance a flash has to pass is very short, the air is not condensed by it and the flash descends straight.

Lightning destroys life when it passes through the body of men or animals, by its violent action on the nerves; it therefore possesses a degree of peril for us which makes some of its properties, and the laws which direct it, matters of important knowledge.

Lightning in seeking the earth will always choose the best conductors, and will leap from a bad conductor to a good one. It also seeks a path by the highest object; or rather, perhaps, it is high objects which discharge the electrical cloud. It is well, therefore, to know which are the conductors that are especially beloved by the fiery visitor. Water is an excellent conductor; so are metals of all kinds. Vapour is a good conductor; the body of man itself is another, the lightning passing through the human fluids. It is therefore unwise to stand near or under a tree in a thunderstorm, because the tall tree would attract the lightning, and as the man would be the better conductor, the flash would diverge from the tree to him; but if he were at a sufficient distance the tree might save him from the flash, because it would be higher and would draw the lightning to itself.

It is dangerous to lean against a wall, because the electric fluid will sometimes run down it, and would leave the wall for the better human conductor.

All sorts of metals are good conductors, and therefore attract lightning; they should not be worn at the time of a storm nor taken in the hand.

A crowd conducts lightning, the vapour arising from it increasing the conducting power of the air above.

Metals conduct in the following order: copper is the best conductor; zinc is next in power; iron next; and lead least.

Iron houses would be safest to inhabit, because the metal walls would draw the lightning from their inmates to the ground. Iron bedsteads are also safest in lightning storms, as they are excellent conductors, and the lightning would prefer the iron pathway to one through the human body. For the same reason the knights of old were safe in their steel armour, which lightning would prefer to the knight himself as a road to the earth, which it seeks.

This power of conducting electricity has caused the placing of lightning conductors by churches, powder magazines, and other public buildings. But these conductors must be of proper size and kept in perfect order, as if broken, cracked, or defective, the electric fluid will fly from them to the building. It is safer not to sit near the fireplace in a thunder-storm, and the middle of the room is to be preferred. Mattresses and beds are non-conductors, and therefore afford security. Silk is a non-conductor, and glass; therefore glass windows protect from lightning in a storm. Pieces of metal of all kinds attract it, and are dangerous. Wet is a protection; wet clothes will conduct lightning from the human body, but it is dangerous to stand near water.

The electric fluid makes itself felt in our dairies and cellars. It produces a disturbance in the condition of milk which turns it sour; and if our beer be new and its fermentation not complete, lightning will so accelerate the process that it will turn the sugar which is not yet alcohol into acetic acid, and we shall have sour beer. Old beer and strong porter, the fermentation of which is more advanced, will be less affected, if at all.

But lightning, in spite of its peril for us, is a beneficent agent in creation. It is one of the great sources of heat. It purifies the air by producing nitric acid* in it, and by agitating the air-currents.

* Nitric acid acts very powerfully in destroying noxious exhalations from putrid vegetable or animal matter. It is formed by the electric fluid chemically uniting the nitrogen and oxygen of the atmosphere.

A thunder-storm generally follows very dry weather in summer. The dry air being a non-conductor will not relieve the clouds of it, and they are at length discharged in a storm ; whereas moist air or falling rain - a good conductor - carries the fluid silently, and by degrees, from the clouds into the earth.