2. 夜間視力 - 見つける、見えなくする

Vision at night differs in degree, also, according to the concentration of attention; in this connection, the following principles are from my own experience:

1. When you follow with your eyes a thing once discovered, you will be able to see it for a long distance.

2. The distance at which you first discover an object, is less than the distance where you loose sight of it. Therefore, at night, if you lose sight of an object you have once discovered, it is difficult to find it a second time. When you follow it with your eye vision is easy, -and the distance at which the object is visible becomes much greater, especially if there are supplementary indications. In such a case a thing liable to be unnoticed, will be seen by the observer.