So Urbain is thankful for the new model atom, and says that “Bohr, in reviving our hopes, is a great benefactor.” Adding, “It seems necessary either to resign ourselves to not understanding, as Bohr has done, or to resign ourselves to a model in flagrant violation with experience.” Those sufficiently resigned to not understanding I now ask to return with me for a short and final visit to those suburban stellar districts situated some three hundred thousand light-years from our sun, where matter is moving ever faster and faster away from us. By a strange contradiction, time in those regions seems to be moving slower and slower, as if tired with the long journey and no longer able to keep up the killing pace set by the stars. Light, too, appears to be losing the race. Professor Michelson, of the University of Chicago, established the velocity of light not long ago at 299,796 kilometers per second--roughly 186,000 miles. But now Monsignor E. J. Gheury de Braye, in an article in _L’Astronomie_, official organ of the Astronomical Society of France, declares that the velocity of light decreases by four kilometers every second. We may perhaps grasp a moment’s understanding by saying that this is relativity, that light merely travels slower in comparison with the quickened pace of time and matter in the outer stellar spaces. This, however, will not serve us long, for W. de Sitter, the Dutch astronomer, taking all these things into consideration, must needs offer an “explanation.” “The world of de Sitter,” says Wirtz in summing it up, “is a four-dimensional continuum of space and time, forming the surface of a sphere in five-dimensional co-ordinates.” If you look wise and pretend in scientific circles that you understand this, you go to the foot of the class. A four-dimensional sphere with a surface in five-dimensional co-ordinates does not pretend to be comprehensible. To declare it to be graspable by the human mind is to insult it. But it can be used in equations, like any other “imaginary” quantity, though--again like any other imaginary quantity--it is quite unimaginable. Imaginary quantities are not such awesome nonentities. Anybody can make a few for himself and play with them as well as can anybody else. Let us take nothing to begin with, thus--0. Write a 2 under it--0/2. We have now one-half of nothing. Now multiply a cipher by 2, and we have twice nothing, or 2(0)--not for a moment to be confounded with twenty. Then one half of 2(0), or twice nothing, equals two times 0/2, or one-half of nothing, because each is equal to nothing at all and things which are equal to the same thing are equal to each other--and for various other reasons.