  In this section the experiment performed by Matthew Meselson and Franklin Stahl, which has been called “the most beautiful experiment in biology”, and which was designed to answer the question of the correct DNA replication mechanism will be discussed (Meselson and Stahl 1958). Meselson and Stahl described their proposed method. “We anticipated that a label which imparts to the DNA molecule an increased density might permit an analysis of this distribution by sedimentation techniques. To this end a method was developed for the detection of small density differences among macromolecules. By use of this method, we have observed the distribution of the heavy nitrogen isotope \(\ce{^{15}N}\) among molecules of DNA following the transfer of a uniformly \(\ce{^{15}N}\)-labeled, exponentially growing bacterial population to a growth medium containing the ordinary nitrogen isotope \(\ce{^{14}N}\)” (Meselson and Stahl 1958, pp. 671–672).