The first neutrino detector ever built is a tank containing 100,000 gallons of perchloroethylene (cleaning fluid) in the cavity 4,850 feet below ground in the Homestake Mine in Lead, South Dakota. Ray Davis, Jr., principal scientist of the experiment, is leaning on the catwalk above the tank and J. Galvin, expert technician, is standing below. The photograph is by courtesy of the Brookhaven National Laboratory (circa 1967) and is taken from Figure 10.3 of the book "Neutrino Astrophysics" by John Bahcall.