[2][3] Harkins researched the structure of the atomic nucleus and was the first to propose the principle of nuclear fusion,[4][5] four years before Jean Baptiste Perrin published his theory in 1919-20.

[5] Harkins was born in Titusville, Pennsylvania, and graduated with a PhD from Stanford University in 1907.

In the beginning of the 1930s, Harkins constructed the second ever cyclotron with fellow University of Chicago scientist Robert James Moon, improving greatly on the design of the previous one.

Among other University of Chicago scientists who made use of this cyclotron was Enrico Fermi, who performed neutron diffusion experiments.

[9] Since 1978, the magnet yoke of the cyclotron Harkins built has been on display at Fermilab.Harkins was elected to the United States National Academy of Sciences in 1921 and the American Philosophical Society in 1925.