Page:Popular Science Monthly Volume 42.djvu/445

Rh terminal, and can be transmitted to the brain through the same nerve-fiber. From Lippmann's recent researches on The Photography of Color it appears that all parts of the spectrum can now be photographed on films of albumino-bromide of silver to which two aniline substances, azaline and cyanine, have been added. It seems, therefore, reasonable to suppose that a relatively small number of substances could enable all rays of the visible spectrum to affect the retina. It seems to me that the question becomes narrowed down to this, Do the nerve-impulses arise from mere vibration or from chemical change in the molecules of the nerve terminal? The photo-chemical hypothesis has much in its favor. We know how rapidly light can induce chemical change in photographic films, and we know that light induces chemical change in the vision purple in the outer segments of the rod-cells of the retina. The fatigue of the retina produced by bright light is best explained on a chemical theory, but it could also be explained on a mechanical theory; for we must remember that even if the nerve-impulses produced in the visual cells were merely a translation of the energy of light into vibration of nerve-molecules, the nerve-impulse has to pass through layers of ganglionic cells before reaching the fibers of the optic nerve, and in these cells it probably always induces chemical change. I have endeavored to place before you a subject that involves physical and physiological considerations of extreme difficulty. I have not attempted to solve the difficulties, but rather to show their nature."

Work of the Forestry Division.—The year 1891, according to chief Fernow's report, witnessed greater activity and interest in forestry than any previous year. A bulletin, What is Forestry? issued by the division, showed that the forestry interests of this country rank second, if not first, in the value of our annual products reaching the market. The largest share of the expenditure of funds as well as of attention was bestowed upon investigations into the character of our timber trees, or "timber tests." These relate to a judgment of mechanical properties from a simple microscopic or macroscopic examination, and to the determination of the relation in which structure, physical conditions, and mechanical properties stand to the conditions under which the tree is grown. A wide and deep interest is manifested in this work throughout the country. In connection with it a study has been made of the lumber pines of the Southern States, the results of which are given in the present report of the chief of the division. The revision of the botanical and the common names of our arborescent flora is nearly completed and will soon be ready for publication. Distributions have been made of packages of seeds of nine important conifers to State agricultural experiment stations, and twenty species of important conifers and deciduous trees to general applicants, besides seeds of the Australian tan-bark wattle to applicants in the Gulf States, the arid Southwest, and the southern part of the Pacific coast region.

The Forerunners of Matches.—Besides the primitive devices for fire-making, Mr. Walter Hough, in a paper on that subject, describes several that were used in civilized countries before matches became universal. The brimstone match is found in Japan as a broad, thin shaving tipped with sulphur; in Mexico it is a cotton wick dipped in sulphur. These are used to catch the sparks from flints or steels. The "spunk," or splint tipped with sulphur, was in common use in this country prior to 1825, and lingered in out-of-the-way places long after the introduction of matches. In parts of France it is still in use with the briquet or tinder box. A variation of the spunk match was curled shavings tipped with sulphur. Attempts to supersede the clumsy briquets produced the tinder piston, the tinder wheel, and later the first chemical match. The first employment of phosphorus was by dipping the match into a bottle full of phosphorous mastic mixed with oxide of phosphorus. The next was the "instantaneous light box," "eupyrion," "dip splint," or, in the United States, "match-light box"—a tin box or wooden receptacle, containing a glass bottle filled with asbestus soaked with sulphuric acid, and wood splints tipped with sulphur and then dipped in a paste made of chlorate of potash, powdered sugar, and gum arabic, with water. The "prometheans" were tubes of glass filled with sulphuric acid, surrounded with an inflammable mixture