Abstract: Method of underwater arc welding comprising the steps of placing a welding electrode nearby a parent material to be welded, immerged in water; generating a high frequency voltage between the electrode and the parent material for starting a striking arc and supplying a high frequency current to said electrode, after said striking arc has been initiated; generating a welding voltage for producing a weld at the parent material and; simultaneously sustaining the high frequency current, superimposed to the welding current, for stabilizing said welding arc during the time duration of the underwater arc welding.

Abstract: Residual aqueous phases, emanating from the synthesis of methyl chloride by reacting methanol with hydrochloric acid, are conveniently demethanolized by maintaining same in liquid phase and in the absence of catalyst, at a temperature of from 50.degree. to 150.degree. C. and under a pressure of less than about 8 bars. The methanol recovered is in the form of a crude methyl chloride which is advantageously recycled to the CH.sub.3 OH/HCl reaction zone.

Abstract: The invention relates to the technical field of pilotage aids for helicopters. In a speed measuring device having two measuring devices for longitudinal speed and lateral speed of the helicopter, each measuring device comprises a single sensor (9a, 9b) for sensing the position of the cyclic rotor pitch control along the axis concerned, and for sensing the acceleration component along the same axis. Each measuring device further includes a computer to provide the air speed components of the helicopter. Applications include flight testing, and the construction of firing computers and flight computers.

Abstract: A method for obtaining information relating to material contained in geological formations. According to this method; these geological formations are subjected to at least one flow of so called incident neutrons having a substantially well defined energy, the incoherent inelastic diffusion spectrum of the diffused neutrons resulting from the interaction of the incident neutrons with the material contained in the geological formations is established at least partially, and from this spectrum are inferred certain of the energy amounts frequently transferred between the incident neutrons and molecules of the materials contained in the formations, or vice versa.

Abstract: The method and device make use of an alternate two-way radiotelegraph link for establishing a communication between a transmitting station and a receiving station. Transmission of messages is synchronous and is performed by means of the error self-correction coding technique and the technique which involves repetition of the coded message or part of the message.

Abstract: The method comprises the steps of heating a sample of sediments, determining a group of two parameters S.sub.1 and S.sub.2 which represent, respectively, the amounts of at least one hydrocarbon compound and of at least one oxygen-containing compound formed by heating the organic material contained in the sediment, and evaluating from the determination of this group of parameters the capacity of the sediments to constitute a good mother rock (i.e. source) for hydrocarbons.