For a few years past, oxygen has been employed in therapeutics; it is found in commerce either in a gaseous state or in solution in water (in siphons); it notably relieves persons afflicted with asthma or depression; and the use of it is recommended in the treatment of albumenuria. Does it cure, or at least does it contribute to cure, anaemia, that terrible affection of large cities, and the prime source of so many other troubles? Here the opinions of physicians and physiologists are divided, and we limit ourselves to a mention of the question without discussing it. Only fifteen years ago it would have been folly to desire to obtain remunerative results through the electrolysis of water. Such research was subordinated to the industrial production of electric energy. We shall not endeavor to establish the priority of the experiments and discoveries. The question was in the air, and was taken up almost simultaneously by three able experimenters--a Russian physicist, Prof. Latchinof, of St. Petersburg, Dr. D'Arsonval, the learned professor of the College of France, and Commandant Renard, director of the military establishment of aerostation at Chalais. Mr. D'Arsonval collected oxygen for experiments in physiology, while Commandant Renard naturally directed his attention to the production of pure hydrogen. The solutions of the question are, in fact, alike in principle, and yet they have been developed in a very different manner, and we believe that Commandant Renard's process is the completest from an industrial standpoint. We shall give an account of it from a communication made by this eminent military engineer, some time ago, to the French Society of Physics. _Transformations of the Voltameter._--In a laboratory, it is of no consequence whether a liter of hydrogen costs a centime or a franc. So long as it is a question of a few liters, one may, at his ease, waste his energy and employ costly substances.