But our task is not, even now, complete. The finishing touch to the explanation of the rainbow was given by the eminent Astronomer Royal, Sir George Airy. Bringing the knowledge possessed by the founders of the undulatory theory, and that gained by subsequent workers, to bear upon the question, Sir George Airy showed that, though Young’s general principles were unassailable, his calculations were sometimes wide of the mark. It was proved by Airy that the curve of maximum illumination in the rainbow does not quite coincide with the geometric curve of Descartes and Newton. He also extended our knowledge of the supernumerary bows, and corrected the positions which Young had assigned to them. Finally, Professor Miller of Cambridge and Dr. Galle of Berlin illustrated with careful measurements with the theodolite the agreement which exists between the theory of Airy and the facts of observation. Thus, from Descartes to Airy, the intellectual force expended in the elucidation of the rainbow, though broken up into distinct personalities, might be regarded as that of an individual artist, engaged throughout this time in lovingly contemplating, revising, and perfecting his work. The white rainbow (_l’arc-en-ciel blanc_) was first described by the Spanish Don Antonio de Ulloa, lieutenant of the Company of Gentleman Guards of the Marine. By order of the King of Spain, Don Jorge Juan and Ulloa made an expedition to South America, an account of which is given in two amply illustrated quarto volumes to be found in the library of the Royal Institution. The bow was observed from the summit of the mountain Pambamarca, in Peru. The angle subtended by its radius was 33° 30′, which is considerably less than the angle subtended by the radius of the ordinary bow. The white rainbow has been explained in various ways. The genius of Thomas Young throws light upon this subject, as upon so many others. He showed that the whiteness of the bow was a direct consequence of the smallness of the drops which produce it. The smaller the drops, the broader are the zones of the supernumerary bows, and Young proved by calculation that when the drops have a diameter of 1-3000th or 1-4000th of an inch, the bands overlap each other, and produce white light by their mixture. SNOW, HAIL, AND DEW --ALEXANDER BUCHAN