  Hacking also remarks on the “noteworthy observations” on Iceland Spar by Bartholin, on diffraction by Hooke and Grimaldi, and on the dispersion of light by Newton. “Now of course Bartholin, Grimaldi, Hooke, and Newton were not mindless empiricists without an ‘idea’ in their heads. They saw what they saw because they were curious, inquisitive, reflective people. They were attempting to form theories. But in all these cases it is clear that the observations preceded any formulation of theory” (Hacking 1983, p. 156). In all of these cases we may say that these were observations waiting for, or perhaps even calling for, a theory. The discovery of any unexpected phenomenon calls for a theoretical explanation.