Maurice de Broglie (1875-1960), 6th duc de Broglie, was a leading French physicist and the elder brother of Nobel laureate Louis de Broglie. Trained as a naval officer (top of his École navale class, 1895), he turned to experimental physics and established a private laboratory in Paris, where he developed X-ray spectroscopy and observed the first absorption edge. His work on high-frequency X-ray spectra and the nuclear photoelectric effect (discovered in 1921) earned him international recognition. Elected to the Académie des sciences in 1924 and the Académie française in 1934, he held the chair of General and Experimental Physics at the Collège de France (1942-1945), and presided over the Académie des sciences in 1954. It is in this dual capacity as scientific and academic authority that he prefaces Robert Richard-Foy's Voyages interplanétaires et énergie atomique (1947).