in from falling. I believe that a stream of
negative particles is being liberated into the air near here, and
allowed to drift where it will. That was my theory when I had the
First Air Division equipped with those dust ejector tubes.

"I knew that if such a condition existed, the positively charged dust
would be pulled down toward the source of the negative particle
stream, which must, in many ways, resemble a cathode ray. That was why
I wanted the behavior of the dust clouds watched and reported. What I
did not foresee was that the iron and steel parts of the plane,
accumulating a heavy negative charge, would be magnetized enough to
slow down the motors and eventually wreck the ships."

"We have had eight ships wrecked unexplainably within twenty miles of
here, all of them to the south, during the past year," said Colonel
Wesley.

"It had slipped my notice. At any rate, the behavior of the ships this
afternoon showed me that my theory is correct, and that some such
device exists and is in active operation. Our next task is to locate
it and destroy it."

"You shall have every man on the Proving Ground!" cried Colonel
Wesley.

"Thank you. General Merton, will you detach three ships from the First
Air Division by radio and have them report here? I want two pursuit
ships and one bomber, with a rack of hundred-pound demolition bombs.
All three must have duralumin cylinder blocks."

"I'll do it at once, Doctor," the general agreed.

"Thank you. Carnes, telephone Washington for me. Tell Dr. Burgess that
I want Tracy, Fellows and Von Amburgh, with three more men down here
by the next train. Also tell him to have Davis rig up a demagnetizer
large enough to demagnetize the motors of a transport plane and bring
it down here to fix up General Merton's ship. When you have finished
that, get hold of Bolton and ask for a dozen secret service men. I
want selected men with Haggerty in charge."

"All right, Doctor. Shall I tell Miss Andrews to come down as well?"

* * * * *

Dr. Bird frowned.

"Certainly not. Why would she come down here?"

"I thought she might be useful, Doctor."

"Carnes, as you know, I dislike using women because they can't control
their emotions or their expressions. She would just be in the way."

"It seems to me that she saved both our lives in Russia, Doctor, and
but for her, you wouldn't have come out so well in your last adventure
on the Aberdeen marshes."

"S