"It never occurred to me that the Periodic System should begin precisely with hydrogen." Whose words do you think these are? They would be most likely to come from one of the legion of investigators or amateurs who set themselves the task of drawing up a new periodic system all of their own or of rearranging it to suit themselves. The diversity of "periodic systems" that made their appearance was no smaller than of notorious perpetual motion machine projects.

   Well, the phrase in quotation marks was written by none other than D. Mendeleyev. It appeared in his famous "Foundations of Chemistry," a textbook used in its time by tens of thousands of students. Now why was the author of the Periodic Law
mistaken? In his time there were all grounds for such mistakes. The elements were then arranged in the Table in order of increasing atomic weight. The atomic weight of hydrogen is 1.008, of helium is 4.003. Hence, why not assume that there might be elements with atomic weights of 1.5, 2, 3, and so on? Or elements lighter than hydrogen, with atomic weights smaller than unity?

   Mendeleyev and many other chemists thought this to be quite possible. And they were supported by the astronomers, representatives of a science very far removed from chemistry. We daresay, their support was involuntary. It was the astronomers that first proved new elements to be discoverable not only in the laboratory and not only by analysing terrestrial minerals.

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