I returned to the hives on the 4th, as I had forgotten to bring the queen excluder with me on the previous day. The queen excluder is a wire mesh frame that goes between the hive bodies and the honey supers. The mesh is large enough to allow the worker bees to get into the honey supers, but small enough to not allow the queen to pass. Thus, we don't get any eggs in the honey that we are planning to eat.
Unfortunately, when I opened the top cover, I discovered that the foundation in the frames in the honey super had all fallen out. I had not done a very good job of installing the wax foundation into the frames. A frustrating and unneccesary setback, chalked up to inexperience. I removed the super and all the frames, and re-installed new wax foundation, hopefully the right way this time.