Gravitational force is simple, and a thing by itself, as also are electric and magnetic forces as long as the electric and magnetic poles stand at rest. But as soon as motion comes into the picture, the whole situation is changed. Forces of new kinds come into play, for moving electric charges exert magnetic forces in addition to the electric forces they exert when at rest, while moving magnets exert electric forces in addition to the magnetic forces they exert while at rest. When the exact laws governing these intricate laws had been discovered by a great number of experimenters, Clerk Maxwell succeeded in expressing them in a mathematical form which was both simple and elegant.

Superficially at least the forces of electricity and magnetism seem to present the same kind of problem as gravitation. Experiment shows that two electrically …

At this time, space was supposed to be filled with an ether, a substance which might well serve, among other functions, to transmit forces across space. So lon…

The human race, whose intelligence dates back only a single tick of the astronomical clock, could hardly hope to understand so soon what it all means.

The motion of the stars over our heads is as much an illusion as that of the cows, trees and churches that flash past the windows of our train.

'Now! Dasher, now! Dancer, now! Prancer, and Vixen, 'On! Comet, on! Cupid, on! Dunder and Blixem; 'To the top of the porch! to the top of the wall! 'Now dash a…

Don't fight forces, use them.