The vacant expression of the eyes is very peculiar, and at once shows when a man is completely lost in thought. Professor Donders has, with his usual kindness, investigated this subject for me. He has observed others in this condition, and has been himself observed by Professor Engelmann. The eyes are not then fixed on any object, and therefore not, as I had imagined, on some distant object. The lines of vision of the two eyes even often become slightly divergent; the divergence, if the head be held vertically, with the plane of vision horizontal, amounting to an angle of 2° as a maximum. This was ascertained by observing the crossed double image of a distant object. When the head droops forward, as often occurs with a man absorbed in thought, owing to the general relaxation of his muscles, if the plane of vision be still horizontal, the eyes are necessarily a little turned upwards, and then the divergence is as much as 3°, or 3° 5’: if the eyes are turned still more upwards, it amounts to between 6° and 7°. Professor Donders attributes this divergence to the almost complete relaxation of certain muscles of the eyes, which would be apt to follow from the mind being wholly absorbed.[906] The active condition of the muscles of the eyes is that of convergence; and Professor Donders remarks, as bearing on their divergence during a period of complete abstraction, that when one eye becomes blind, it almost always, after a short lapse of time, deviates outwards; for its muscles are no longer used in moving the eyeball inwards for the sake of binocular vision. Perplexed reflection is often accompanied by certain movements or gestures. At such times we commonly raise our hands to our foreheads, mouths, or chins; but we do not act thus, as far as I have seen, when we are quite lost in meditation, and no difficulty is encountered. Plautus, describing in one of his plays[907] a puzzled man, says, “Now look, he has pillared his chin upon his hand.” Even so trifling and apparently unmeaning a gesture as the raising of the hand to the face has been observed with some savages. Mr. J. Mansel Weale has seen it with the Kafirs of South Africa; and the native chief Gaika adds, that men then “sometimes pull their beards.” Mr. Washington Matthews, who attended to some of the wildest tribes of Indians in the western regions of the United States, remarks that he has seen them when concentrating their thoughts, bring their “hands, usually the thumb and index finger, in contact with some part of the face, commonly the upper lip.” We can understand why the forehead should be pressed or rubbed, as deep thought tries the brain; but why the hand should be raised to the mouth or face is far from clear.