Slide showing two line charts demonstrating two equations. Slide shows two line charts demonstrating two equations. Title below charts reads: 'Fig 2. In these figures, the observations of a particular experiment are plotted in duplicate and the two figures can be superimposed on one another so that every point on one figure falls exactly on the corresponding point on the other. It is obvious that only data of a very high order of accuracy would enable us to assess the relative value of the two equations, although it will be noted that one curve inflects when X = 1/2a, while the other inflects when X = 1/3a.' Late 19th to early 20th century