May those men who are animated by the true scientific spirit cease to believe that they are obliged to consider only subjects of public utility;... because, one must not hide it, the field of applications, so rich and fertile today, would not take long to be blighted by sterility if it ceased to be fertilized and revivified by the beneficial light which theoretical research radiates and pours incessantly upon it.

As quoted in The Life and Science of Léon Foucault : The Man Who Proved the Earth Rotates (2003) by William Tobin, p. 93.