A similar case is Hubble's measurement of the expanding Universe. The Universe is expanding, and Hubble's linear velocity = Hubble_constant*distance law is an excellent first approximation, but:
1. Hubble was actually measuring the local motion of nearby galaxies, the so called Local Group. These galaxies are too close for Hubble expansion to matter, they're just gravitating.
2. The actual value for the Hubble constant he measured was way off, by something like 10x.
1. Hubble's draftsman made an error while preparing his famous diagram. From Figure 1 of his paper (http://adsabs.harvard.edu/abs/1931ApJ....74...43H), you'll notice that the vertical axis is in "km" rather than "km/sec."
2. Measurements of the Hubble Constant over time: http://www.pnas.org/content/101/1/8/F2.large.jpg For some reason it's not plotted logarithmically so it's hard to see the convergence towards ~70 km/s/Mpc in the last twenty years.
Interestingly, there was a long fight in the field of cosmology from ~1960 until ~1990 as to whether the Hubble constant was 50 or 100. It wasn't until within the past twenty years or so that the community began to agree upon the now-accepted value of ~70 km/s/Mpc.
1. Hubble was actually measuring the local motion of nearby galaxies, the so called Local Group. These galaxies are too close for Hubble expansion to matter, they're just gravitating.
2. The actual value for the Hubble constant he measured was way off, by something like 10x.