tty tall
order even for you, Tom Swift!"

[Illustration: "That Sounds Like a Tall Order!"]

"Let's go back in the lab and I'll tell you more about the project."

Tom directed Koku to carry the telescope inside. As the three walked
back, the giant suddenly gave a yell.

"Quick, Master!"

With that the servant let go the big instrument, placing it with a thud
none too gently on the hard ground. In a bound he was off. Tom and Ned
caught a glimpse of someone just disappearing around the edge of the
building. Had the stranger sneaked into the laboratory while Koku's
back was turned?

[Illustration: Koku Bounded Off]

"I hope the space eye isn't smashed!" exclaimed Tom, examining the
instrument. "Or the telescope lens."

Anxiously Ned waited as his chum detached the green disk and held it up.

"I--I guess it's O.K.," said Tom at length. "I'll test it in the lab and
see."

[Illustration: "I Hope the Space Eye Isn't Smashed!"]

At this moment Koku reappeared, saying the intruder had vanished.
Moreover, he was very contrite about having handled the telescope
roughly. In a few seconds the fears of the three vanished. Put to the
electric test, the disk was found to be all right.

"Who do you suppose was sneaking around here?" asked Ned.

"No telling," replied Tom. "But nothing seems to be missing," he added,
glancing around.

[Illustration: "Nothing Seems to Be Missing."]

"I hope you're right," said Ned. "Now tell me more about this green
disk. How did you happen to discover the stuff?"

"As to just what it is," replied the other slowly, "I'm not sure yet.
When I analyzed it, I found a substance absolutely new to chemistry."

"Where did you get it?" asked Ned.

"I scraped it from that meteorite down in Koku's country in South
America."

Ned whistled. "Ever since we found that thing which we called a planet
stone, you've been discovering all sorts of things about it."

[Illustration: "I Scraped It From a Meteorite."]

"Right now I hope to revolutionize the field of astronomy with it," said
Tom.

"Tell me more about this wonderful green substance."

"It may be a new compound or it may be an unknown element. Anyway, in
experimenting with it I found that heat and electricity both change the
stuff. The former has an apparently permanent effect, while an electric
current, as you saw, alters it only temporarily."

[Illustration: "Heat and Electricity Change It."]

"Why didn't you make a big disk? Then yo