I put into a room various kinds of wild birds, which had been taken in nets after they were full grown. The window, which looked upon a garden, was unglazed, and closed by a wire netting, through which the outer air entered and was constantly renewed. I placed in the middle of the room a pot containing a shrub of some size, on which the birds used to perch. Since they had been reared in the open air they were certainly accustomed to the wind, and to the way in which it moves trees and branches, so that they were not alarmed by a phenomenon which they recognized from experience. I fastened a cord to the head of the shrub which I passed through a hole in the door, making another to look through, and in this way I moved it to and fro as the wind might have done. One day when there was a high wind which could be heard in the room, and when the current of air through the window was perceptible, I tried the experiment when the conditions of resemblance were perfect. And yet when the violent movement and oscillation of the shrub was combined with the noise of the wind, the frightened birds all fluttered about, and after repeating the movement, and then allowing it to subside, they kept away from the shrub and did not dare to settle on it. At another time, aided by an ingenious young friend, I constructed a toy windmill, of which the vanes were moved by weights. I placed this toy in a cage, so arranged that its motions could be regulated from the outside, and I put into the cage a sparrow, which had been taken from the nest, and which consequently had no experience of the external world. Much patience was needed, since the toy required careful adjustment and was easily thrown out of gear, but I managed it at last. The sparrow pecked at the little mill as soon as he was put into the cage, and he grew up accustomed to its motions. I then took the sparrow out of the cage and put in a finch, which had also been taken from the nest, but was reared far from such a machine, and he was frightened and did not reconcile himself to it for some time. I exchanged this bird for a goldfinch which had been caught after he was full grown, and his alarm at the little mill was so great that he did not dare to move.