On the other hand, there are scientists of high eminence, such as Dr. Robert A. Millikan, our oldest living Nobel-Prize-winner in physics, who doubt whether the H-bomb can be made at all. And there are also those who express the view that, while it probably could be made, it would not offer advantages great enough, if any, to justify the cost in vital strategic materials necessary for our security. Fortunately, facts mostly buried in technical literature make it possible for us to go behind the scientific curtain and look intimately at the reasons for these differences in opinion. More important still, these facts not only provide us with a clearer picture of the nature of the problem but also enable us to make some reasonable deductions or speculations. The scientists directly involved do not feel free to discuss these matters openly, not because they would be violating security, but because of the jittery atmosphere that acts as a damper on open discussion even of subjects known to be non-secret. We already know that the so-called hydrogen bomb, if it is to be made at all, cannot be made of the abundant common hydrogen of atomic mass one, and that there are only two possible materials that could be used for such a purpose: deuterium, a hydrogen twin twice the weight of common hydrogen, which constitutes two hundredths of one per cent of the hydrogen in all waters; and a man-made variety of hydrogen, three times the weight of the lightest variety, known as tritium. We also know that to explode either deuterium or tritium (also known, respectively, as heavy and superheavy hydrogen) a temperature measured in millions of degrees is required. This is attainable on earth only in the explosion of an A-bomb, and therefore the A-bomb would have to serve as the fuse to set off an explosion of deuterium, tritium, or a mixture of the two.