It is the lighting of a lamp or the observed effect of some...

It is the lighting of a lamp or the observed effect of some other test which tells us that electricity works. Until the work of Isaac Newton no one knew anything about the mutual attraction of bodies which Newton expressed in his equations of gravitation. Gravitation cannot be seen, makes no sound, cannot be felt, tasted, or smelt. But since Newton, the laws of gravity have been part of the basic concepts with which science calculates. All our new industries make use of it.

Yet Newton himself never saw the force which he quantified so ably. It was observing the fortuitous fall of an apple from a tree that drew his attention to it. Physicists make great use of spectroscopy. They reckon the colours of the spectrum as ranging from red at the bottom to violet at the top. But they also acknowledge that innumerable colours exist both below red and above violet, all imperceptible to us. Colour varies with wave-length, they tell us. And the wave-lengths are waves of light.

The sun's light, or light from any other source, is composed of the combination of all the colours in a single ray, and 'white' in particular is the impression that the mix generally makes upon our optics. When these rays strike an object, that object absorbs a proportion of the rays and reflects back the rest. It is the reflected rays we see and by them we observe the object. Moreover, colours change and differ in proportion to the weakness or strength of the wave.

If the force of the wavelength reaches 457,000 milliards per second, the light moves into the red band; at 727 thousand milliards, into the violet band; while there are uncountable hues, shades, and saturations of colour and tint both above and below these figures which are beyond human perception. The air which surrounds us has an extraordinary weight of its own. Its pressure on our bodies is a steady 16,000 kilograms.

Because the pressures outside and inside the body are equal, we fell no discomfort. Before the days of Galileo Galilei (1564-1642) and Bliaise Pascal (1623-1662) this scientific fact was unknown. Nor could it ever have been recognised from the sense. Certain observed phenomena, like the variation in air pressure at different altitudes, drove thinkers to devise a hypothesis of the weight of air and then to devise experiments to test and prove it.

[Our 4th Imam 'Ali Zaynu 'l-Abidin as-Sajjad in the 55th Litany of Vol.