Signalling across space without wires / being a description of the work of Hertz & his successors

A technical lecture and extended essay presents Hertz's experimental demonstration of electromagnetic radiation and follows subsequent laboratory work and engineering attempts to detect and exploit those waves. It explains radiation, absorption, and syntony, reproduces key experiments with oscillators and detectors (including Branly filings tubes, the coherer, and early telephone receivers), and examines phenomena such as reflection, refraction, and polarization. Later sections survey adaptations for wireless telegraphy, report demonstrations by several investigators, and trace the historical and practical development of coherer-based signalling, with appendices summarizing related photoelectric research and practical remarks on apparatus and patents.