talline form. And the kind of crystals a substance makes are not
too specific about what the substance is, but they tell a great deal
about what it cannot be. In the fractionator slide he could get more
information--the rate-of-diffusion of a substance in solution ruled
out all but a certain number of compounds that it could be. The two
items together gave a definite clue.

Another voice from the speaker:

"_Headquarters! Paras are massing by the north gate! They act ugly!
They're trying to force their way into Government Center! We'll have
to start shooting if we're to stop them! What are our orders?_"

The grid operator said dully:

"They'll wreck everything. I don't want to live because I'm a para,
but I haven't acted like one yet. Not yet! But they have! So they
don't want to be cured! They'd never forget what they've done. They'd
be ashamed!"

Calhoun punched keys on a very small computer. He'd gotten an
index-of-refraction reading on crystals too small to be seen except
through a microscope. That information, plus specific gravity, plus
crystalline form, plus rate of diffusion in a fractionator, went to
the stores of information in the computer's memory banks somewhere
between the ship's living quarters and its outer skin.

A voice boomed from another speaker, tuned to public-broadcast
frequency:

"_My fellow-citizens, I appeal to you to be calm! I beg you to be
patient! Practice the self-control that citizens owe to themselves and
their world, I appeal to you...._"

Outside in the starlight the Med Ship rested peacefully on the ground.
Around and above it the grid rose like geometric fantasy to veil most
of the starry sky. Here in the starlight the ground-car communicators
gave out the same voice. The same message. The President of Tallien
Three made a speech. Earlier, he'd made another. Earlier still he'd
taken orders from the man who was already absolute master of the
population of this planet.

Police stood uneasy guard about the Med Ship because they could not
enter it. Some of their number who had entered the control building
now stood shivering outside it, unable to force themselves inside
again. There was a vast, detached stillness about the spaceport. It
seemed the more unearthly because of the thin music of wind in the
landing grid's upper levels.

At the horizon there was a faint glow. Street lights still burned in
the planet's capitol city, but though buildings rose against the sky
no lig