"Considérations sur les Résultats d'un Allégement Indéfini des Moteurs." In: JOURNAL DE PHYSIQUE THEORIQUE ET APPLIQUÉE, 5e série, tome III (Mars 1913). Paris: Au Bureau du Journal de Physique, Mars 1913. Octavo, single issue, original blue wrappers printed in black, untrimmed. Esnault-Pelterie's lecture on "considerations on the results of unlimited lightening of engines," delivered in 1912 in both St. Petersburg and Paris, was the first to demonstrate theoretically that space travel was possible; it marks the beginning of theoretical astronautics. "The lecture contains all the theoretical bases of self-propulsion, destroying the myth that rockets need atmospheric support and giving the real equation of motion. Anticipated is the use of auxiliary propulsion for guidance and complete maneuverability of rockets. Also contained are calculations of the escape velocity, the phases of a round-trip voyage to the Moon, and the times, velocities, and durations, of trips to the Moon, Mars, and Venus, as well as thermal problems related notably to the surface facing the sun ... This 1912 lecture is the first purely scientific study marking the birth of astronautics. While Tsiolkovsky had the prescience and talent to first suggest, in 1903, rocket propulsion to space, REP was the first to develop the equations of the problem and to establish the mathematical theory of interplanetary flight. REP is thus the founder of theoretical astronautics" (Blosset, p. 9). As noted above, the use of rockets for space travel had been discussed by the Russian scientist Konstantin Tsiolkovsky (1857-1935) in his 1903 paper, "Exploration of Cosmic Space by Means of Reaction Devices," as well as in an earlier paper published in 1896. However, Tsiolkovsky's work was published only in Russian and it remained almost completely unknown to Western scientists until the 1920s. Esnault-Pelterie did not know of Tsiolkovsky's rocketry work in 1912, but had become aware of it by 1930; see the historical introduction (pp. 17-38) of his L'ASTRONAUTIQUE. Esnault-Pelterie's lecture first appeared in print in the JOURNAL DE PHYSIQUE THEORIQUE ET APPLIQUÉE, but in abridged form, due to both space considerations and the trepidation of the journal's editor, who was shocked by Esnault-Pelterie's ideas on space travel. "REP deplored the exaggerated condensation of the lecture, which was the cause for an apparent divergence between Goddard's and his own opinions concerning the possibility at the time of building vehicles capable of escaping from the earth's gravitation. In fact, Goddard wanted only to send a projectile loaded with powder to the moon and observe its arrival by telescope. REP considered the conditions necessary for transporting living beings from one celestial body to another and returning them to the earth; his more pessimistic conclusions were based on considerations of the substantial initial mass required for a rather small final mass, in view of the limited means available at the time" (Blosset, p. 9). Blosset, "Robert Esnault-Pelterie: Space pioneer," in Durant and James, First Steps toward Space (Washington DC: Smithsonian Institution Press, 1974), pp. 5-31; pp. 23-31 contain an English translation of the unabridged lecture. Interlibrum 270 #112. Norman 713. Von Braun and Ordway, History of Rocketry and Space Travel, pp. 74-75. Spine panel restored, a very good copy of a very delicate work printed on inferior wood pulp paper. Rare. (#135078).