their illusions were due to an imagination beyond their control. *
Successful palming in these more difficult cases usually involves the practice of all the methods for improving the sight described in succeeding chapters. For reasons which will be explained in the following chapter, the majority of such patients may be greatly helped by the memory of a black object. They are directed to look at such an object at the distance at which the color can be seen best, close the eyes and remember the color, and repeat until the memory appears to be equal to the sight. Then they are instructed, while still holding the memory of the black, to cover the closed eyes with the palms of the hands in the manner just described. If the memory of the black is perfect, the whole background will be black. If it is not, or if it does not become so in the course of a few seconds, the eyes are opened and the black object regarded again.
Many patients become able by this method to see black almost perfectly for a short time; but most of them, even those whose eyes are not very bad, have great difficulty in seeing it continuously. Being unable to remember black for more than from three to five seconds, they can not see black for a longer time than this. Such patients are helped by central fixation. When they have become able to see one part of a black object darker than the whole, they are able to remember the smaller area for a longer time than they could the larger one, and thus be come able to see black for a longer period when they palm. They are also benefited by mental shifting (see Chapter XV) from one black object to another, or from one part of a black object to another. It is impossible to see, remember, or imagine anything, even for as much as