D O C U M E N T 2 9 O P T I C A L E X P E R I M E N T 4 7 2. This narrower version for possible consideration may be characterized as a “surveyable combination of a gyroscopic kymograph with a device for observing the direction of apparent gravity” (more precisely, its projection on an aircraft plane and lateral plane). That this combination has a certain value and in the customary sense is worth protecting, likewise that it appears for the first time in the Anschütz patent seems hardly doubtful to me. That for Anschütz the device to indicate the direction of apparent gravity is itself a part of the kymograph, while for Drexler it is not, does not seem to me to constitute an essential difference. Even with this[11] interpretation perhaps coming into consideration, Drexler’s steering indicator falls within the scope of protection of the plaintiff’s patent. I therefore cannot acknowl- edge as legitimate the decision offered at the bottom of page 9 of Wolff’s expert opinion even in case 2 of the narrower scope—unless the combination of gyro- scopic kymograph and vertical reference indicator generally is not regarded as war- ranting protection. Wolff’s expert opinion does not draw this possible interpretation of the reach into consideration at all. sig. A. Einstein. Berlin, 18 January 1920.[12] 29. “On an Optical Experiment Whose Result Is Incompatible with the Undulatory Theory” [Berlin, around 19 January 1922][1] Theoretical part by A. Einstein, experimental part by H. Geiger and W. Bothe. [2] Theoretical Part (A. Einstein) In a notice that recently appeared in these Berichte, I took under consideration an optical experiment that promised to deliver interesting conclusions about the findings regarding the elementary process of light emission.[3] Messrs. Geiger and Bothe performed this experiment at the Physikalisch Technische Reichsanstalt with the secure result that the diffraction required by the undulatory theory of light emit- ted by canal-ray particles in dispersive media does not occur.[4] The importance of this finding prompts me in the following to preface a description of the experi- ments with a more precise presentation of the a few considerations related to it. In our current investigations theories about light, two hitherto not connectable theoretical systems run independently alongside each other, both apparently indispensable and yet irreconcilable with each other contradictory to [p. 1]