Introduction
dimensions of space-time are necessary to account for the observed phenomena of nature, and there are some suggestions of the necessity for more than four. It is only when dealing with very high velocities, such as are comparable with the velocity of light, that the unity of time with space thrusts itself upon the notice of physicists, for even with such a velocity as that of the planet Mercury in its orbit it is only after the lapse of centuries that any divergence from the motion strictly calculated on the basis of Euclidean Geometry and Newton's laws of gravitation and of motion has become apparent. The observed behaviour of electrons, moving in high vacua with velocities comparable with the velocity of light, has confirmed some of Einstein's conclusions and necessitated a revision of our fundamental notions of kinematics and the laws of motion when these high velocities are concerned. But the whole subject of Relativity has strongly appealed to popular interest through the brilliant confirmation of Einstein's theory of gravitation by the bending of light in passing close to the sun's surface and the consequent apparent displacement of stars which are very close to the sun from their true relative position when photographed during a solar eclipse. The best popular exposition of the whole subject of relativity and gravitation is to be found in Professor Eddington's Space, Time, and Gravitation.
But when a great truth comes to light it is generally found that there have already been prophets crying in the wilderness and preparing the way for the reception of the Revelation when the full time has come. In an anonymous letter published in Nature on February 12th, 1920, entitled "Euclid, Newton, and Einstein," attention was called to such a prophet in the following words:—
"Some thirty or more years ago, a little jeu d'esprit was written by Dr. Edwin Abbott, entitled 'Flatland.' At the time of its publication it did not attract as much attention as it de-
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