e gravitational field about even two suns
is so exceedingly complex that a planet could take up an orbit only
such that one sun was at each of the two foci of the ellipse of its
orbit, and then only provided the suns were of very nearly the same
mass, and stationary, which in turn means they must have _no_ attraction
for each other. No, I think his complex system of seventeen suns would
not be so good for planets. Celestial Mechanics won't let them stay
there. And I really don't see why it was necessary to have so complex a
system.

Further, I wonder if Dr. Smith considered the proposition of his ammonia
cooling plant carefully? The ammonia "cooling" plant works only to
_transmit_ heat, not to remove it. The heat is removed by it from the
inside of an icebox for instance, and put outside, which is what is
wanted. However, it must have some place to dump the heat. In the fight
with the Mardonalians, Seaton has an arenak cylinder on his compressor,
and runs it very heavily, but if he can't get the heat outside the ship,
and away from it, he wouldn't cool the machine at all. Since the
Mardonalians kept the outside so hot, and the story says the
compressor-cooling was accomplished by a water cooler which boiled--some
amount of water, too, if it would absorb all the heat of that
Mardonalian fleet in any way--and this heat was then merely transferred
from outside to inside--where they DIDN'T want it!

Again, in this battle, to protect themselves against ultra-violet
radiation, they smear themselves with _red_ paint--presumably because
red will stop ultra-violet.

Personalty, I'd have picked some ultra-violet paint--if any were handy
as that would _reflect_ the rays. Red wouldn't affect them at all, so
far as I can see--he might as well have used blue. What he wanted, was a
complementary color of ultra-violet, and I don't believe it is
red--green is the complement of red. (Green light won't pass through red
glass.)

Dr. Smith invited "knocks" with that foreword of his--I hope I am
complying, as an interested reader, and a hopeful scientist. However, my
personal opinion has always been that "Skylark of Space" was the best
story of scientifiction ever printed, without exception. I have recently
changed my opinion, however, since "Skylark Three" has come out.

John W. Campbell, Jr.

Cambridge, Mass.

(This letter from a fellow author is an excellent comment on Dr. Smith's
foreword to "Skylark Three." But the writer of