“We were able to discover two new kinds of atomic species, one was hydrogen of mass 3, unknown until that time, and the other helium of mass 3, also unknown.”
On his research on atomic nuclei with Ernest Rutherford, p. 24
Portraits in Science interviews (1994)
Context: We were able to discover two new kinds of atomic species, one was hydrogen of mass 3, unknown until that time, and the other helium of mass 3, also unknown. … We were able to show that heavy hydrogen nuclei, that is to say the cores of heavy hydrogen atoms, could be made to react with one another to produce a good deal of energy and new kinds of atom. …Of course, we had no idea whatever that this would one day be applied to make hydrogen bombs. Our curiosity was just curiosity about the structure of the nucleus of the atom, and the discovery of these reactions was purely, as the Americans would put it, coincidental.
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Mark Oliphant 6
Governor of South Australia (1971-76) 1901–2000Related quotes

"Talk with the American Correspondent Anna Louise Strong"(August 1946)
Source: Something More, A Consideration of the Vast, Undeveloped Resources of Life (1920), p. 58

Audio lectures, Creationism and Psychology (n. d.)

Department of Defense news briefing (12 February 2002)
Variant:
Now what is the message there? The message is that there are no "knowns." There are things we know that we know. There are known unknowns. That is to say there are things that we now know we don't know. But there are also unknown unknowns. There are things we do not know we don't know. So when we do the best we can and we pull all this information together, and we then say well that's basically what we see as the situation, that is really only the known knowns and the known unknowns. And each year, we discover a few more of those unknown unknowns.
:It sounds like a riddle. It isn't a riddle. It is a very serious, important matter.
:There's another way to phrase that and that is that the absence of evidence is not evidence of absence. It is basically saying the same thing in a different way. Simply because you do not have evidence that something exists does not mean that you have evidence that it doesn't exist. And yet almost always, when we make our threat assessments, when we look at the world, we end up basing it on the first two pieces of that puzzle, rather than all three.
:* Extending on his earlier comments in a press conference at NATO Headquarters, Brussels, Belgium (6 June 2002) http://www.nato.int/docu/speech/2002/s020606g.htm
2000s

Source: The Story Of The Bible, Chapter X, The Position Today, p. 133

The New Marvel in Photography (1896)
Context: Having discovered the existence of a new kind of rays, I of course began to investigate what they would do. … It soon appeared from tests that the rays had penetrative power to a degree hitherto unknown. They penetrated paper, wood, and cloth with ease; and the thickness of the substance made no perceptible difference, within reasonable limits. … The rays passed through all the metals tested, with a facility varying, roughly speaking, with the density of the metal. These phenomena I have discussed carefully in my report to the Würzburg society, and you will find all the technical results therein stated.

"The Big Higgs Question" http://www.nybooks.com/daily/2012/07/09/big-higgs-question/, The New York Review of Books, 9 July 2012