Note 23 — Front matter (continued 7)

It is supposed by many, that when the spark is long enough we can note the direction in which it travels; and observations of the motion of lightning from the earth to the cloud have been collected, as showing that the usually observed direction of the flash is sometimes reversed. In reality, no one has ever seen a lightning flash travel either one way or the other. If the attention is fixed on the storm cloud, as usual when a lightning storm is watched, every flash appears to pass from the cloud to the earth. If, on the contrary, at the moment when the attention is fixed on some terrestrial object the lightning flashes near that particular object, the flash will seem to pass from the object to the cloud. In either case the motion is apparent only. If there is motion at all, the passage of the electric spark occupies less than the 100,000th part of a second, and of course it is utterly impossible that any eye could tell at which end of its track the flash first appeared. In every case the flash seems to travel from the end to which attention was more nearly directed. The apparent motion corresponds to the chance direction of the eye.