"See," Helen explained, "you can easily put double glass sides on your tank by slipping sheets of glass inside the four present outer sides, leaving a space of five or six inches between them. Fill this space with water, and put the goldfish in that. Then they can swim around, and Lizzie can't get at them because they'll be protected by the glass."
She made a sectional view of the tank with its double sides and held it up triumphantly to Joe.
"Will that solve the puzzle?" she asked.
"Why, I really believe it will!" exclaimed Joe, after a moment's thought. "Yes, I could have metal clips, made water-tight with rubber, fitted inside the tank. Taking five inches off each side wouldn't mean much loss. Then I could slip four sheets of glass down in the metal clips, and, as you say, fill the intervening space with water for the goldfish."
"Exactly," cried Helen. "The audience can't tell whether the fish are in the tank with you or not, for the water and glass, being transparent, will make it look exactly as if you and the fish and the seal were in the same bit of water."
"Good!" cried Joe. "I'll do it! The very thing, Helen!"
The fact that persons looking directly at a glass tank of water can not tell how far back the water and tank extends is taken advantage of by moving picture operators in producing novel effects. Only the other day was shown a scene where a man apparently went down to the bottom of a river. Fish swam all about him, there was a portion of a wreck half buried in the sand and mud, and waving aquatic plants seemed to reach out and twine themselves around the man, while fish swam above and below him.
This effect was produced by having the man go through certain actions behind a square glass tank in which the sand, aquatic plants, wreck and fish had been placed. The fish could swim about, but the man was not in the water at all but behind the tank, the water and glass offering no obstruction to the camera.
It was that principle which Helen suggested to Joe. He and the seal would be doing their act behind a glass and water screen, in which fish were swimming and aquatic plants gently waving.
Joe lost no time in putting the plan into operation. He ordered the glass and metal holding clips, with the water-tight rubber gaskets, from the same firm in New York that had originally made Benny's tank. They still had the patterns, and knew just the proper size and kind of glass to send, and Joe had no difficulty in malting his tank a double one.