atom of hydrogen was one charge of positive electricity balanced by one charge of negative. At least, he guessed that if you could ever get a hydrogen atom off by itself, it could be called a balance. But it was not a perfect balance, for the touch of fire would make the moon slip off and combine with the moons of oxygen in a sharp explosion.

An atom of helium was heavier, as if four positive charges were balanced by four negatives. Rutherford did not tell the young mind just how those four positive charges—which would naturally fly apart—were cemented into the nucleus, but Marvin guessed that two of the negatives did the work, leaving two moons in the sky. This balance was very strong. The gas never burns or explodes, and can be pressed into a liquid so cold that it boils far below the point where mercury freezes.

A girl composed entirely of helium would be perfectly neutral, incapable of sending out one flash or thrill. All the girls he knew were composed of flesh and blood, which of course were chemical substances but very far from neutral.

Now at last he understood what those flashes of light from the radium had been and still were, for the bombardment was steadily going on there in the dark corner of the hospital. They were the reflection of helium atoms that had lost two moons and came shooting out of the radium to find them. They would pick up the two missing satellites and again become the quiet inert gas. What bully stuff to put in a balloon, if only there were enough of it!

He wondered just how much electricity lay packed in the nucleus of a radium atom. The nucleus of every atom evidently carried a charge, an excess of positive over negative. He used to go up into the den, from which his father was generally absent, and think about it. He would pick up that old sieve of phosphor bronze and tilt it to an angle of thirty degrees and look at the minerals in the cabinet. If he could only get a spectrum from the positive electricity concealed in the heart of each atom, he could number the elements from hydrogen up. Just now they went by weights, but ought not cobalt to come before nickel, even if it was heavier? Cobalt was more like iron, and ought to come right after iron.

Chapter 3. Lithium

He had chosen Yale in the hope of sometime studying under Boltwood, the chemist who first perceived that the metal radium slowly changes into lead. As a mere freshman he presented himself in Dr. Boltwood’s office, was sharply questioned, was recognized as being 

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