This paper concentrates on a debate over dispersion in the second half of the 1830s, in which both sides utilized the same set of experimental data to test a proposed wave account of dispersion, but could not agree on how these data should be used. The conflict regarding experimental data was caused by differences in instruments. In the debate, optical instruments in many ways functioned like paradigms, shaping scientists' opinions. Instruments also led the debate into an impasse, because no apparatus (...) was available for the necessary experimental replication. Because of unreconcilable differences regarding experimental evidence, the wave theory's failure in explaining dispersion did not become an obstacle to its acceptance. (shrink)