(*31) Common experiments in Natural Philosophy. If two red rays from two luminous points be admitted into a dark chamber so as to fall on a white surface, and differ in their length by 0.0000258 of an inch, their intensity is doubled. So also if the difference in length be any whole-number multiple of that fraction. A multiple by 2 1/4, 3 1/4, &c., gives an intensity equal to one ray only; but a multiple by 2 1/2, 3 1/2, &c., gives the result of total darkness. In violet rays similar effects arise when the difference in length is 0.000157 of an inch; and with all other rays the results are the same—the difference varying with a uniform increase from the violet to the red. “Analogous experiments in respect to sound produce analogous results.” (*32) Place a platina crucible over a spirit lamp, and keep it a red heat; pour in some sulphuric acid, which, though the most volatile of bodies at a common temperature, will be found to become completely fixed in a hot crucible, and not a drop evaporates—being surrounded by an atmosphere of its own, it does not, in fact, touch the sides. A few drops of water are now introduced, when the acid, immediately coming in contact with the heated sides of the crucible, flies off in sulphurous acid vapor, and so rapid is its progress, that the caloric of the water passes off with it, which falls a lump of ice to the bottom; by taking advantage of the moment before it is allowed to remelt, it may be turned out a lump of ice from a red-hot vessel. (*33) The Daguerreotype. (*34) Although light travels 167,000 miles in a second, the distance of 61 Cygni (the only star whose distance is ascertained) is so inconceivably great, that its rays would require more than ten years to reach the earth. For stars beyond this, 20—or even 1000 years—would be a moderate estimate. Thus, if they had been annihilated 20, or 1000 years ago, we might still see them to-day by the light which started from their surfaces 20 or 1000 years in the past time. That many which we see daily are really extinct, is not impossible—not even improbable. Notes—Maelstrom (*1) See Archimedes, “_De Incidentibus in Fluido_.”—lib. 2. Notes—Island of the Fay (*1) Moraux is here derived from moeurs, and its meaning is “fashionable” or more strictly “of manners.” (*2) Speaking of the tides, Pomponius Mela, in his treatise “De Situ Orbis,” says “either the world is a great animal, or” etc (*3) Balzac—in substance—I do not remember the words (*4) Florem putares nare per liquidum aethera.—P. Commire. Notes — Domain of Arnheim