In my description of Venus in Lucky Starr and the Oceans of Venus, I had a planetwide ocean, which, at that time, seemed at least possible. It was essential to the plot as well. However, we now know that the surface of Venus is at a temperature far above the boiling point of water, and an ocean – or even a drop – of liquid water on its surface is totally impossible.

As for Mars, in my book David Starr: Space Ranger, I managed to get the description right in many ways. However, I didn’t take advantage of the huge extinct Martian volcanoes that were discovered about fifteen years after the book was published. What’s more, I did talk about the canals (dry ones), which were found to be nonexistent, and I introduced intelligent Martians remaining from a long-dead surface civilization, and this is really extremely unlikely.

Jupiter and its satellites appeared in Lucky Starr and the Moons of Jupiter, and while I was careful to describe all the worlds, I naturally missed some major points that were not discovered till twenty years afterward. I said nothing of the cracked world-girdling glacier of Europa and nothing of Io’s active volcanoes. I didn’t mention Jupiter’s huge magnetic field. Nor, in Lucky Starr and the Rings of Saturn, did I mention some of the interesting features of the Saturnian satellite system and rings.

The only book in the series that survived intact (scientifically speaking) was Lucky Starr and the Pirates of the Asteroids.

Fortunately, there was a way out. Honesty in the best policy and when the Lucky Starr series was reprinted in the 1970s, I insisted on inserting introductory notes explaining where the astronomical details had become outdated. At first, the publishers were a little reluctant to do so, but I explained that I could not allow the young reader to be misled, or, if he were knowledgeable, to have him think that I was not. In went the notes, and, I am glad to say, sales were not adversely affected.

None of the stories in this collection was as badly shattered as my poor Lucky Starr books were, but there are things to beware of.

In the first place, there is one place where I missed something that was (in hindsight) very obvious, and I have been kicking myself over it for the last couple of years.

In "The Martian Way," the same story in which I triumphed with my description of the spacewalk, I had my heroes approach Saturn and actually enter the ring system. In doing so I very carefully described the rings, making use of observations from Earth’s surface to do so.

Now, from Earth’s surface, some 800 million miles from Saturn, we see the rings as solid and unbroken except for the black line of the Cassini division that seems to separate them into two rings. The portion of the rings closest to Saturn is considerably dimmer than the rest of the ring system, and that portion is usually considered a third ring (the so-called "crepe ring.") And that was how I described the rings as seen by my space-travelers in the story.

Yet it stands to reason (at least, now it stands to reason) that if we could see the ring system from a nearer distance, we would see greater detail. We would see divisions – places where fewer particles were in orbit so that we would see dimmer lines separating brighter lines – divisions that would simply not be seen at great distances. Earth’s surface telescopes would just blur them out and record only the thickest of the dim lines – the Cassini division.

The closer we would get, the more numerous and the thinner the bright lines would get as visibility became clearer and clearer, until, when we were as close as we could get and still see all the rings, the rings would look like a grooved record – which is what they do look like.

Suppose I had figured this out in 1952 and had described the rings in that fashion. Even if I had missed such things as shadowy "spokes" in the ring, and "braided" rings, things that were absolutely unpredictable, it would have been great if I had imagined the fine divisions. That was an easy deduction to make and if I had described the rings in that fashion then, as soon as those rings had been probed I would have announced that I had anticipated what they had discovered. (You think that modesty would have held me back? Don’t be an idiot!) How great that would have been! As it is, my failure to see this marks me down as not very bright, and that is there, for all to see, in "The Martian Way." To be sure, no astronomer saw the truth about the rings in 1952, but what of that? An astronomer is only an astronomer and his vision is naturally limited. I am a science fiction writer and more is expected of me.

Then, too, sometimes when I saw accurately, or when I saw something that might well prove to be accurate some day, then I generally placed it far too far into the future. I admit I got the robots correct, for my earliest stories indicated that they got their start in the 1980s and 1990s, which is not bad at all.

However, what of the computerized cars in "Sally" and of the pocket computers in "The Feeling of Power"? I was careful not to give the exact dates of discovery of these advances. (I may be dumb, but I’m not that dumb.) Still, there’s no doubt as we read the stories that they are discoveries of the far future – yet they’re here now and I have lived to see them, and be embarrassed over my lack of confidence in the human mind and human ingenuity.

"Breeds There a Man…?" deals, in part, with the development of an advance against the nuclear bomb. It was published in 1951 and, although I don’t date it, the impression it gives is that its events take place in the near future, perhaps just a few years after 1951.

I was clearly wrong in this, for real discussions of possible defenses didn’t come till the 1980s.

What’s more, my notion of a defense was a purely static one – the creation of a force-field shield strong enough to resist even a nuclear explosion (the story was written before the H-Bomb was invented, by the way). Now that we are considering a nuclear defense, we are talking of an active one. We are talking of the use of computerized X-ray lasers, designed to shoot down intercontinental ballistic missiles as soon as they are launched and move beyond the atmosphere. Frankly, I don’t think this will work either, but it is considerably more advanced than my own foolish speculation of the matter in 1951, thirty-five years ago.

Generally, I can do my best foreseeing once I’m given a hint (a good strong hint). In my robot stories, I postulated robots that were so huge that they were immobile and that could do nothing but think and communicate the results of those thoughts. I had one like that in my very first robot story. In later robot stories I called them "brains." I didn’t think to call them computers.

My robots, too, had "brains" that made them work, and I never spoke of them as computers, either. I had to make them science-fictionish, of course, so I called them "positronic brains." Positrons had been detected for the first time only four years before my first robot story had been written.

Positrons were exciting particles, bringing with them visions of "antimatter." For that reason, I thought positronic brains was a phrase that sounded good. They would not be essentially different from electronic brains, except that positrons could be made to come into being and would then be destroyed in a millionth of a second or so by all the electrons that surround them, no matter where on Earth they were. That gave me the notion that they might be seen as responsible for the rapidity of thought. To be sure, the energy relationships – the energy required to produce positrons in quantity or the energy released when positrons are destroyed in quantity – are horrendous, so great that the notion of positronic brains is forever impossible, in all likelihood – but I ignored that.