RECOLLECTIONS AND REFLECTIONS
may be last in the moving one. Thus, for example, if a woman after the bkth of one child moved into a different neighbourhood before the birth of a second, she might appear to have had twins to an observer in a moving system, while to an observer in a system moving more rapidly the second child would appear to have been born before the first. One wonders what the mother would have thought of relativity. The paradox, however, ceases when we remember that, as an observer of an event at a distance does not observe it at the time it occurs, but only after the interval required by light to travel to him from the scene of the event, his knowledge of distant events must always be out of date. Thus if he is observing two events at two different places, one nearer to him than the other, then though the events occurred simultaneously at the two places, he would perceive that at the place nearer to him before he did that at the other. When the observer is moving, his distances from the two places change, and if he is moving so as to approach the place that was at first further away and recede from the other, when he came to the place where the distances were equal, then simultaneous events would take the same time to reach him and he would regard them as simultaneous, and when he went still further, the one that was at first perceived after the other would now precede it.
The results arising from the principles of relativity were so surprising, and its exposition by Einstein so masterly, that it excited the interest and admiration of mathematicians and also of the general public to an extent which had never even been approached by any other mathematical question. Lectures on it attracted large audiences, books about it became " best sellers", and one was continually being asked by one's neighbour 430