When Rob had been hugged and kissed by his mother and sisters, and even Mr. Joslyn had embraced him warmly, he gave them a brief account of his adventures. The story was received with many doubtful looks and much grave shaking of heads, as was quite natural under the circumstances.  
"I hope, my dear son," said the father, "that you have now passed through enough dangers to last you a lifetime, so that hereafter you will be contented to remain at home."
 
"Oh, Robert!" cried his mother, with tears in her loving eyes, "you don't know how we've all worried about you for the past week!"
 
"A week?" asked Rob, with surprise.
 
"Yes; it's a week to-morrow morning since you flew into the air and disappeared."
 
"Then," said the boy, thoughtfully, "I've reached home just in time."
 
"In time for what?" she asked.
 
But he did not answer that question. He was thinking of the Demon, and that on the afternoon of this very day he might expect the wise and splendid genius to visit him a second time.
 
At luncheon, although he did not feel hungry, he joined the family at the table and pleased his mother by eating as heartily as of old. He was surprised to find how good the food tasted, and to realize what a pleasure it is to gratify one's sense of taste. The tablets were all right for a journey, he thought, but if he always ate them he would be sure to miss a great deal of enjoyment, since there was no taste to them at all.
 
At four o'clock he went to his workshop and unlocked the door. Everything was exactly as he had left it, and he looked at his simple electrical devices with some amusement. They seemed tame beside the wonders now in his possession; yet he recollected that his numerous wires had enabled him to strike the Master Key, and therefore should not be despised.
 
Before long he noticed a quickening in the air, as if it were suddenly surcharged with electric fluid, and the next instant, in a dazzling flash of light, appeared the Demon.
 
"I am here!" he announced.
 
"So am I," answered Rob. "But at one time I really thought I should never see you again. I've been—"
 
"Spare me your history," said the Demon, coldly. "I am aware of your adventures."
 
"Oh, you are!" said Rob, amazed. "Then you know—"
 
"I know all about your foolish experiences," interrupted the Demon, "for I have been with you constantly, although I remained invisible."
 
"Then you know what a jolly time I've had," returned the boy. "But why do you call them foolish experiences?"
 
"Because they were, abominably foolish!" retorted the Demon, bitterly. "I entrusted to you gifts of rare scientific interest—electrical devices of such utility that their general adoption by mankind would create a new era in earth life. I hoped your use of these devices would convey such hints to electrical engineers that they would quickly comprehend their mechani............