z Amonar on the way--no, get them to Tellus,
too. Then we'll get action quicker. Those four are all I want--get
anybody else you want to come along."

His hands playing over the keys of an enormous calculating machine,
Brandon was instantly immersed in a profound mathematico-physical
problem; deaf and blind to everything about him. Westfall, knowing well
that far-reaching results would follow Brandon's characteristic attack,
sat down at the controls of the communicator. He first called Mars, the
home planet of Alcantro and Fedanzo, the foremost force-field experts of
three planets; and was assured in no uncertain terms that those rulers
of rays were ready and anxious to follow wherever Brandon and Westfall
might lead. Thence to Venus, where Dol Kenor, the electrical wizard,
and Pyraz Amonar, the master of mechanism, also readily agreed to
accompany the expedition. He then called the General-in-Chief of the
Interplanetary Police, requesting a detail of two hundred picked men
for the hazardous venture. These most important calls out of the way,
he was busy for over an hour giving long-distance instructions so that
everything would be in readiness for the servicing of the immense
space-cruiser the following Tuesday night.

Having guarded against everything his cautious and far-seeing mind
could envisage, he went over to Brandon's desk and sat down, smoking
contemplatively until the idea had been roughed out in mathematical
terms.

"Here's the rough draft of the ray screen, Quince. We generate a blanket
frequency, impressed upon the ultra carrier wave. That's old stuff, of
course. Here's the novelty, in equation 59. With two fields of force,
set up from data 27 to 43, it will be possible actually to project a
pure force of such a nature that it will react to de-heterodyne the
blanketing frequency at any predetermined distance. That, of course,
sets up a barrier against any frequency of the blanketed band.
Incidentally, an extension of the same idea will enable us to see
anywhere we want to look--calculate a retransmitting field."

"One thing at a time, please. That screen may be possible, but
those fields will never generate it. Look at datum 31, in which your
assumptions are unsound. In order to make any solution at all possible
you have assumed cosine squared theta negligible. Mathematically, it is
of course vanishingly small compared to the first power of the cosine,
but fields of that type must be _exact_, and your