Meselson and Stahl designed an experiment that would allow them to discern wheth

Meselson and Stahl designed an experiment that would allow them to discern whether DNA replication occurs in a dispersive, semiconservative, or conservative manner.
They started with E. coli that had been growing for many generations in medium containing 15N.
They then transferred the bacteria into medium containing only 14N, and allowed the bacteria to undergo two rounds of DNA replication.
After each round of replication, the scientists performed density-gradient centrifugation of the DNA.
The scientists reasoned that each of the three models would predict different DNA banding patterns after the two rounds of replication.