Few substances have been made the subject of experimental inquiry more frequently than the compounds of phosphorus and hydrogen, and no subject is so remarkable for the various and conflicting results which it has presented to chemists of the greatest acuteness and practical skill. The obscurity which long hung over the subject has been dispelled, however, in a great measure, by the recent investigations of Henry Rose of Berlin. Although baffled in his early researches, that philosopher returned again and again to the subject, and at last succeeded in determining the chemical functions and true constitution of phosphuretted hydrogen. He has shewn it to be analogous to ammonia in chemical character and composition. But hitherto two compounds of phosphorus and hydrogen had generally been admitted to exist, which were believed to differ in composition, as they do in properties, one being spontaneously inflammable in atmospheric air, and the other not so. Rose establishes beyond all doubt that these gases are essentially of the same composition, and of the same specific gravity; and, indeed, that they are mutually convertible, each into the other, without any addition or subtraction of matter that could be perceived. In explanation of their possessing different properties, under the same composition, allusion is made by Rose to Isomerism, or the doctrine that two bodies may exist identical in composition, but differing in properties. Certainly the existence of two gases, constituted alike, and yet possessing different properties, if established, would afford a firm basis for this doctrine.