But the trick lies in combining fresh and salt water so that the egg will sink only half-way.
Make a strong brine solution by dissolving common table salt in water. It may be necessary to experiment a little before getting the solution just the right strength. Fill a glass fruit jar, or any jar with a wide opening, half full of the brine. Now, with a funnel, pour fresh water in on top of the salt water. Be careful not to let the two kinds of water mix. The salt water, being heavier, will be on the bottom of the jar, and the fresh, being lighter, on top. If you do it carefully enough, pouring in a little fresh water at a time, you will have, as Joe had, a jar with two layers of different kinds of water—one salt, the other fresh. The audience, of course, can not see this, as they could if you had two differently colored fluids, for the salt and fresh water are of the same color.
When Joe put the egg in the water he lowered it carefully, so as not to disturb the two water layers. The egg sank through the strata of fresh water, but when it came to the layer of dense, salt water, it would not sink in that, and came to a stop, half-way down, just as Joe, who knew at what point this would occur, uttered the command to stop.
And when Joe pretended, to dissolve the “spell,” he merely, with his wand, stirred together the fresh and salt water. This made a mixture of salt water, but it was not dense, or heavy, enough to support the egg, which of course sank to the bottom.
And, as the waters were well mixed when Joe let the young man try the experiment, of course the latter could not make the egg float as the boy wizard had done.
“That was a good trick, Joe,” was the professor’s compliment when Joe came off the stage. “In fact I think the simpler the trick is, the better, but there are very few that can be worked with so little apparatus as your egg experiment. We’ll keep that on our list.”
Joe had told his employer about the news brought by Harry, to the effect that our hero was accused of robbery by his foster-parent.
“What are you going to do about it, Joe?” asked the professor.
“I don’t see that I can do anything. I didn’t take a dollar of his money, or Mrs. Blackford’s either, nor did I touch the valuable papers. It’s all a mistake, but I’m not going back there to tell him so. I sent word by Harry. If he won’t believe him, he won’t believe me.”
“No, perhaps not. And, as you say, you can’t go back there just to convince your foster-father. You don’t think, do you, that he will make trouble for you?”