D O C U M E N T 2 8 4 M A Y 1 9 2 6 3 0 3 (c) as above grating 0.05 mm The observed min. & max. agree for (a) & (b) with the computed ones. The rea- son for the interferences not disappearing completely is probably diffraction off the grating & the beam direction (II), which (c) especially suggests as well, an exper- iment in which no min. could be established with certainty, just a general diminish- ing of intensity, which may well be straight-lined, as you indicated. The periodic processes of elect. mag. waves leading to interference must therefore be coupled with periodic processes in the atom (if one does not want to assume that interfer- ence is possible with light-quantum parts from different atoms coupled together). Setup II. Only one lens was used, at whose focus the canal ray was situated. Distance KQ again 1.8 cm.— With this arrange- ment, intensity min. could not be established with certainty, even though that would have been expected. This is perhaps due to the fact that here, in addition to the axially parallel rays, the // rays are also interfering with each other, whereas in setup I, tuned to a telescope set to ∞, only the axially parallel rays exhibit interference max. & min. but all the others exhibit unimpaired interference or ெwhite.” The incomplete vanishing of the interferences in (I) could likewise be explained by this assumption. Setup III, as in (I), but without lenses L1 L2. Center of the interferometer’s dis- tributor plate at 5 cm distance from grating. With this arrangement the interferences are generally substantially more blurred max. & min. could not be established. The indistinctness is probably caused in this case by the ∠ α, coming into consideration for the Doppler compo- nents, being considerably larger than in (I). I hope to be able to report about the mirror-tilt exper- iments soon as well. Respectfully yours, E. Rupp