 Poincaré argued that what survives in theory-change are relations among physical magnitudes, expressed by mathematical equations within theories. His prime example was the reproduction of Fresnel’s laws concerning the relations of amplitudes of reflected rays vis-à-vis the amplitude of incident rays in the interface of two media within Maxwell’s theory of electromagnetism, although in this transition, the interpretation of these laws changed dramatically, from an ether-based account to an electromagnetic-field-based account. For Poincaré