A commercial apparatus containing Neon atoms was used. The tube contained a cathode, two mesh-type control grids (\(G_{1}\) and \(G_{2}\)) , and a collector electrode. The distance between grid 1 and grid 2 was about 5mm. The distance between the cathode and grid 1 and the distance between the collector electrode and grid 2 was approximately 2 mm. The cathode was kept at a constant current (\(135mA\)), and grid 1 and grid 2 were kept at constant voltages. (\(4.8V\) and \(11.6V\) respectively.) The anode current, (converted into \(V_{out}\)), oscillates as accelerating voltage \(U_{2}\) increases. The final Franck-Hertz curve for Neon shown in Figure 3 contained 3 dips of the anode current. Close observation of the peaks and dips indicates a systematic substructure, which can be explained by the excitation of additional energy levels of neon above the lowest excited state. Figure 3 taken from \cite{Rapior_2006} shows 14 excited levels of Neon divided into two groups, \(E_{a1}\) and \(E_{a2}\). If the mean free path is significant, electrons will gain additional energy over \(\lambda\), and will excite states in \(E_{a2}\) and well as exciting the lowest energy level.