Dr. Rich read, and shook Marvin by the hand. “My dear professor, I am glad that one institution does not demand a German doctorate before it recognizes ability. But I can’t make head or tail of what this chemist writes. Mr. Ferry, this heathen language is more in your line.” Asher Ferry put on his eye-glasses and studied the letter. “Well, I get some of it. Marvin is to do no teaching, but is expected to help with administration. Most of his time he will spend in a laboratory. Young man, are you coming back here in August, 1922?” “Certainly.” “Well, there’s going to be trouble about coal before that time. Send me your articles on coal.” “I shall hardly be writing on that subject.” “Then send me whatever you do write. Just put your name on the wrapper, so’s my secretary won’t think it’s from a crank.” “Thank you.” “Marvin, I notice that when we get an invitation and my wife just says thank you, we ain’t a-going.” A faint smile appeared on Marvin’s lips. “Young man,” said Asher Ferry sharply, “if my chemists can’t follow you. I’ll hire one that can. You and I had a pretty good talk on the boat, and you didn’t seem to think me such a damn fool then. I know you ain’t much interested in coal. What you want is to turn some substance into some other substance—change the atoms—and make use of the energy. But there’s one thing I’d like to know before we part. Why has most of the elements got fractional weights?” “Because they are mixtures.” “I don’t understand that.” “Well, weight depends on the nucleus of an atom, and we don’t know much about the pattern of the nucleus yet. But take any atom, and all you need to keep it the same atom is the same balance between nucleus and moons. A nucleus having six positive charges bound by three negative will give lithium just as surely as seven positive bound by four negative. Ordinary lithium is a mixture of a lighter lithium and a heavier lithium.” “Then what’s called pure elements ain’t really pure?” “Probably not. I could tell you more about it if I knew what a chap named Aston has been doing recently in England.” “Well, before you can change one element into another, you’ve got to get it pure, ain’t you?” “Exactly.” “I see. You reckon you’ll spend a few year on fractions?” “I may spend my whole life on them.” “That’s the right spirit, Marvin. Now, whenever you get rid of a fraction, I wish you’d drop me a note. Will you?” “I will.” “Good for you. And now I think I’ll go to bed, if your father will keep me company on the island.” A few minutes later Marvin stopped by the Tarpeian on his way to his canoe. “Darling, I’m off. I don’t blame you for being unwilling to leave your father. May I write to you every day for the next three years?” “I’d rather you wouldn’t. Please don’t write except to say that you have found somebody else.” “Then it will be three years of solid silence. But I’ll be back before your birthday in August, 1922.” Chapter 72. Hafnium