The paper by A. Sommerfeld discusses the propagation of waves in wireless telegraphy, particularly focusing on the role of the Earth in this process. While most practical and theoretical works in wireless telegraphy concentrate on the sender and receiver, the question of wave propagation between them, especially the Earth's role, has received relatively little attention. The author argues that the mechanism of wave propagation is something that experimenters cannot control, while the theory of sender and receiver is relatively simple and well-controlled. Two main types of waves are considered: space waves and surface waves. Space waves are similar to those in acoustics and optics, while surface waves are similar to those in hydrodynamics and certain optical phenomena. The author explores whether the waves in wireless telegraphy are more akin to space waves or surface waves. The paper reviews previous work by Abraham, Uller, and Zenneck, which suggests that the waves in wireless telegraphy are surface waves. These waves are characterized by their reflection at the Earth's surface and their dependence on the properties of both the air and the Earth. The author provides a mathematical framework to support this conclusion, including the introduction of a "numerical distance" that depends on the absolute distance and the material constants of the media involved. The author also discusses the implications of these findings for practical applications, such as the influence of antenna design and the Earth's conductivity on signal transmission. The paper concludes with a comparison of surface waves to electromagnetic waves in conductive media, emphasizing the importance of the Earth's role in the propagation of wireless telegraphy signals.The paper by A. Sommerfeld discusses the propagation of waves in wireless telegraphy, particularly focusing on the role of the Earth in this process. While most practical and theoretical works in wireless telegraphy concentrate on the sender and receiver, the question of wave propagation between them, especially the Earth's role, has received relatively little attention. The author argues that the mechanism of wave propagation is something that experimenters cannot control, while the theory of sender and receiver is relatively simple and well-controlled. Two main types of waves are considered: space waves and surface waves. Space waves are similar to those in acoustics and optics, while surface waves are similar to those in hydrodynamics and certain optical phenomena. The author explores whether the waves in wireless telegraphy are more akin to space waves or surface waves. The paper reviews previous work by Abraham, Uller, and Zenneck, which suggests that the waves in wireless telegraphy are surface waves. These waves are characterized by their reflection at the Earth's surface and their dependence on the properties of both the air and the Earth. The author provides a mathematical framework to support this conclusion, including the introduction of a "numerical distance" that depends on the absolute distance and the material constants of the media involved. The author also discusses the implications of these findings for practical applications, such as the influence of antenna design and the Earth's conductivity on signal transmission. The paper concludes with a comparison of surface waves to electromagnetic waves in conductive media, emphasizing the importance of the Earth's role in the propagation of wireless telegraphy signals.