The density of ground state copper atoms has been measured in an operating large-bore copper laser using hook spectroscopy. In this method, dispersion, due to the copper resonance lines at 327.4 nm and 324.7 nm, is measured by placing the copper laser tube in one arm of a Mach-Zehnder interferometer illuminated by a broad bandwidth UV source. The light source was a Nd:YAG-laser-pumped dye laser which was modified to have a 15 nm bandwidth and then frequency doubled in a 3 mm thick KDP crystal, resulting in a UV beam with an 8 nm bandwidth. The Nd:YAG laser was synchronized with the copper laser, allowing a time resolution of 8 ns. Copper density was measured both as a function of time and as a function of radial position across the bore of the tube. The radial resolution was about 2 mm. The space-dependent data gives information about the gas temperature distribution since the density is inversely proportional to the temperature. The gas temperature distribution found in this way agrees well with the predictions of a simple heat-conduction model which assumes uniform power deposition. The power deposition found in this way was compared to that found by calorimetry.