Page:Arthur B Reeve - The Dream Doctor.djvu/131

 Scarcely a word was spoken as hour after hour Craig sat with the receiver to his ear, connected with the coils down in the storeroom. "You might call this an electric detective," he had explained to Spencer. "For example, if you suspected that anything out of the way was going on in a room anywhere this would report much to you even if you were miles away. It is the discovery of a student of Thorne Baker, the English electrical expert. He was experimenting with high-frequency electric currents, investigating the nature of the discharges used for electrifying certain things. Quite by accident he found that when the room on which he was experimenting was occupied by some person his measuring-instruments indicated that fact. He tested the degree of variation by passing the current first through the room and then through a sensitive crystal to a delicate telephone receiver. There was a distinct change in the buzzing sound heard through the telephone when the room was occupied or unoccupied. What I have done is to wind single loops of plain wire on each side of that room down there, as well as to wind around the room a few turns of concealed copper wire. These collectors are fitted to a crystal, of carborundum and a telephone receiver."

We had each tried the thing and could hear a distinct buzzing in the receiver.

"The presence of a man or woman in that room would be evident to a person listening miles away," he went on. "A high-frequency current is constantly passing through that storeroom. That is what causes that normal buzzing."