Generally speaking, we could continue the Periodic System mentally as far as we liked. The general physical principle of its structure is quite clear. A master-mind once demonstrated a table to one of the present authors, which contained a thousand elements. When asked, "Why a thousand and not two or ten thousand?," the "inventor" replied in embarrassment: "You see, the sheet was not large enough. . ."

   But that was just another oddity. As to the hundred and twenty-sixth element, it can be said quite seriously and definitely that it will belong to a new family of elements, a very singular family, the like of which chemists have never seen.

   The family will begin with element No.121. And all its eighteen members will resemble one another much more, incomparably more than our old friends, the lanthanides. These strange inhabitants of the Big House will hardly differ from one another any more than the isotopes of one and the same element.

   The reason is that the three outer atomic shells of all the elements of the family will be exactly the same; only the fourth-last shell will be filled gradually in the series. Could any perceptible difference in chemical properties be expected in such a case?

   One of the stories of this book is entitled "Fourteen Twins." Now if we tried to describe the properties of the supposed family, we would have to do some hard thinking to find a title for it. Perhaps we might call it "The Eighteen Identical Elements" or "Eighteen Elements, and All as One." The word "twins" is "no go" in this case.

   But since this book is not science fiction, we shall defer concrete descriptions for better times.

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