JAMES Thompson in The Seasons gives a vivid description of a raging thunderstorm:
... and as it nearer comes,
And rolls its awful burden on the wind,
The lightning flashes in a larger curve, and more
The noise astounds, till over head a sheet
Of livid flame discloses wide, then shuts,
And opens wider.
It is the lightning in such a storm, of course, and not the thunder, that is a source of danger, and it may cause damage or injury in a variety of different ways. In the case of inanimate objects, for example, the intense heat following a lightning strike sometimes causes the moisture contained in cavities to boil almost instantaneously; the explosive expansion which accompanies this process may cause damp brickwork to shatter, road surfaces to be ripped apart, or tree trunks to explode. And of course lightning can also cause damage directly by igniting fire.
Buildings can be effectively protected from lightning by means of a sharp rod fixed to their highest point, and connected to earth by means of a stout strip of iron or copper. The lightning conductor provides the easiest path in the vicinity for the great surge of electric current, and allows it to pass harmlessly to earth through the metal strips, with out damage to the structure itself.
In the case of humans, lightning is most likely to kill when the current seeking to find its way to earth passes close to the respiratory centre in the lower part of the brain, or when it passes close to the heart. This situation, in turn, is most likely to occur when the person concerned is standing, upright.
But even if an individual is not directly hit, it is dangerous if lightning strikes nearby. In such circumstances, large voltage differences are created on the ground as the current propagates outwards from the point of contact. This can cause a momentary difference of several thousand volts between the two feet of a person standing in the vicinity, which in turn may result in a potentially fatal surge of electricity through the body; the wider apart the feet, the greater and more life endangering will be the current. For the same reason, we are advised not to lie flat on the ground when threatened by lightning; the safest course is to keep the feet together and crouch as low as possible, adopting an almost foetal position with the hands upon the knees.