A new laboratory has been created at Washington for researches on very low temperatures with the use of liquid hydrogen and liquid helium. I had the honor of dedicating this laboratory to its service. I had the great pleasure of meeting in their laboratories several very important American scientific men. The hours I spent in their company are among the best of my travel. The United States possesses several hospitals for radiumtherapy. These hospitals are generally provided with laboratories for the extraction of radium emanation which is sealed up in small tubes for medical use. These institutions own important quantities of radium, have a very good equipment, and treat a great number of patients. I have visited some of them, and this made me feel more deeply, if possible, the regret of not having in France even one national institute capable of rendering the same services. I hope that this lack will be filled in the near future. The industry of radium has been started in France, but it is in America that it has had its greatest development, owing to the presence of a sufficient supply of the ore carnotite.[15] I was very much interested in my visit to the most important of the factories, and I gladly recognize the spirit of initiative in this undertaking. The factory owns a collection of documentary films which enable one to appreciate the effort made each day in collecting the ore scattered in the immense fields of Colorado, in carrying and concentrating this ore originally very poor in radium. On the other hand, the means of extraction of radium are still the same which have been described in earlier chapters. The greatest courtesy was paid me in my visit to the radium plant and laboratory. I found the same reception at a factory of mesothorium which presented me with some material, and where the officials expressed the desire to help in my scientific work. To make complete these travel impressions it would be necessary to speak of the nature of the country. I recoil before the task, being incapable of expressing in a few words the immensity and the variety of the spaces which opened before my eyes. The general impression is one of unlimited possibilities for the future. I keep a particularly vivid remembrance of the great falls of Niagara, and of the magnificent colors of the Grand Canyon.