The equations of physics contain "constants" such as the speed of light, the value of the charge of the electron or proton, the gravitational coupling constant, the weak coupling constant, the strong coupling constant, Planck's constant, and elementary particle masses. Non-trivial variations in these quantities would not just involve a change of scale caused by a redefinition of units, but would involve the variation with time of certain dimensionless ratios of these sO-{)8l1ed "constants." I will examine the theoretical basis for possible variations in these dimensionless ratios and relate experimental and observational results to place limits on these variations. In particular, I will examine the tunnelling theory of alpha decay and relate it to the possible variation of weak and strong interaction strengths, showing that decay rates may vary without significantly changing the radii of radiohalos. Also, I will examine the data of James Bradley taken in 1727-1747 on the aberration of light from the star gamma Draconis and show that there are extra solar and lunar influences on the nutation of the earth's axis which Bradley unfortunately left out. This suggests that the speed of light in 1727 was the same as it is today. The results will also be related to the author's study of the Roemer method for determining the speed of light (7).
