“But I can’t understand how you are going to do it,” said Mrs. Nestor.  “I’ve read about wireless messages, but I can’t get it through my head.  How is it done, Mr. Swift?”

“The theory is very simple,” said the young inventor.  “To send a message by wire, over a telegraph system, a battery or dynamo is used.  This establishes a current over wires stretched between two points.  By means of what is called a ‘key’ this current is interrupted, or broken, at certain intervals, making the sounding instrument send out clicks.  A short click is called a dot, and a long click a dash.  By combinations of dots, dashes, and spaces between the dots and dashes, letters are spelled out.  For instance, a dot and a space and a dash, represent the letter ‘A’ and so on.”

“I understand so far,” admitted Mrs. Nestor.

“In telegraphing without wires,” went on Tom, “the air is used in place of a metallic conductor, with the help of the earth, which in itself is a big magnet, or a battery, as you choose to regard it.  The earth helps to establish the connection between places where there are no wires, when we ‘ground’ certain conductors.”

“To send a wireless message a current is generated by a dynamo.  The current flows along until it gets to the ends of the sending wires, which we have just strung.  Then it leaps off into space, so to speak, until it reaches the receiving wires, wherever they may be erected.  That is why any wireless receiving station, within a certain radius, can catch any messages that may be flying through the air—­that is unless certain apparatus is tuned, or adjusted, to prevent this.”

“Well, once the impulses, or electric currents, are sent out into space, all that is necessary to do is to break, or interrupt them at certain intervals, to make dots, dashes and spaces.  These make corresponding clicks in the telephone receiver which the operator at the receiving station wears on his ear.  He hears the code of clicks, and translates them into letters, the letters into words and the words into sentences.  That is how wireless messages are sent.”

“And do you propose to send some that way?” asked Mrs. Anderson.

“I do,” replied Tom, with a smile.

“Where to?” Mrs. Nestor wanted to know.

“That’s what I can’t tell,” was Tom’s reply.  “I will have to project them off into space, and trust to chance that some listening wireless operator will ‘pick them up,’ as they call it, and send us aid.”

“But are wireless operators always listening?” asked Mr. Nestor.

“Somewhere, some of them are—­I hope,” was Tom’s quiet answer.  “As I said, we will have to trust much to chance.  But other people have been saved by sending messages off into space; and why not we?  Sinking steamers have had their passengers taken off when the operator called for help, merely by sending a message into space.”

“But how can we tell them where to come for us—­on this unknown island?” inquired Mrs. Anderson.