For, while pacing Bruton Street trying to discover the principles of conduct that threatened to hamper his new power, he had found that in actual operation it was quite simple.

He learned that his mind, in relation to other minds, was like the receiver of a wireless station with an unlimited field.

For, while the wireless could receive messages only from those instruments with which it was attuned, his mind was in key with all other minds.

To read the thoughts of another, he had only to concentrate his own upon that person; and to shut off the thoughts of that person, he had only to turn his own thoughts elsewhere.

But also he discovered that over the thoughts of those outside the range of his physical sight he had no control.