or purpose of the lab; and even so,
many of the experimenters would require continuous monitor observation
from the computer to correct their observations against her
instantaneous error curve.

The mass of water in the rim formed a shell six feet through,
surrounding the laboratories and living quarters--walls, floor and
ceiling--since its first function was that of radiation shielding.

But the bulk of this water was not a single unit. It was divided into
separate streams, twenty in number, in each of which various
biological reactions could be set up.

While a few of the rivers were in a nearly chemically pure state, most
of them were already filling with the plankton and algae that would
form the base of the major ecological experiments, some with fresh
water as their medium, others using sea water, complete with its
normal micro-organisms supplemented from the tanks of concentrate
that Dr. Millie Williams had brought aboard. One or two of the rivers
were operating on different cycles to convert human waste to usable
forms so that it might reenter the cycles of food and air.

Several of the rivers were operating to provide fish and other marine
delicacies as part of the experiment to determine the best way of
converting algae to food in a palatable form.

Within, the rivers were lighted fluorescently--an apparent anomaly
that was due to the fact that the problems of shielding marine life
from direct sunlight in such a shallow medium had not yet been worked
out; while the opaque plastic that walled the laboratories within the
rivers was a concession to their strength, since the clear plastic
that would have provided aquarium walls for the lab and complete
inspection for a constant and overall check of the ecological
experiments had been overruled by U.N. Budget Control. Portholes at
various spots made the seaquariums visible from any part of the rim,
but in Dr. Millie's laboratory alone were the large panels of clear
plastic that gave a real view into the rivers.

This ecological maze of rivers and eddies and balance tanks; of air
jets and current and micro-life; of spin-rate-control and shielding,
were all keyed to servo-regulated interdependence that for this
self-contained world replaced the stability achieved in larger
ecologies through survival mechanisms.

* * * * *

Within the maze, existing by it and contributing to it, were the
laboratories concerned with other things