Published in Nautilus, in 1991, in volume 105, pages 1-6

Published in Nautilus, in 1991, in volume 105, pages 7-15

Published in Nautilus, in 1991, in volume 105, pages 26-37

Published in Nautilus, in 1991, in volume 105, pages 81-91

Published in Nautilus, in 1991, in volume 105, pages 119-146

Published in Nautilus, in 1991, in volume 105, pages 147-151

Published in Nautilus, in 1991, in volume 105, pages 159-164

Published in Nautilus, in 1991, in volume 105, pages 166-172

Published in The Nautilus, in 1991, in volume 105, issue 3, pages 116-117