We develop an intuitive understanding of the effect of gravity because it is more readily apparent than any of the other forces. Newton understood something that was not obvious, that celestial bodies are subject to the same force of gravity that affects matter on earth. It was a step in the direction of understanding that the laws of physics on earth are the same as the laws of physics in the 'heavens'.

Prior to Newton it was not thought that laws could be extrapolated from the earthly to the cosmic scale. His formulation of those laws was so correct that today Newton's laws are used to send rockets into space.

Newton understood that the inertia of an object is a measure of its mass. He formulated three laws of motion. The first states that if a body is at rest or moving at a constant speed in a straight line it will remain like that unless acted on by a force. The second says that the change in motion of a body is proportional to the force impressed. The third states that every action has an equal and opposite reaction.

This work was of signal importance in the formation of a coherent understanding of the forces governing the action of matter. Newton's laws correspond with ‘common sense’ reality. They are clear and concise and invoke a sense of 'obviousness'. This comfortable picture of reality would prevail for 250 years.

For many, history is only any good if you don't live there. Of those honoured and feted in our textbooks only a few were given the time of day in their own lifetimes. Newton was honoured, satirised and praised. His light shines undimmed in the firmament of scientists.

As well as being the least esoteric of the four forces we now recognise, gravity is also the weakest by a huge factor. Before the twentieth century two other forces were on the agenda: magnetism and electricity. Magnetism, the force designed to assist sailors in navigation and decorate fridges, is most readily seen as an attraction between some metals. Electricity is visible in phenomena such as lightning. They are both powerful forces. Electricity is 10,000,000,000,000,000,000,000,000,000,000,000,000 (10 to the power of 37) times stronger than gravity but less easily comprehensible.