Page:Encyclopædia Britannica, Ninth Edition, v. 18.djvu/849

P H P H 813 fishing-lines, <fec., its valuable properties having attracted the attention of traders even before colonists settled in the islands. The leaves, for fibre -yielding purposes, come to maturity in about six months, and the habit of the Maoris is to cut them down twice a year, rejecting the outer and leaving the central immature leaves. Phormium is prepared with great care by native methods, only the mature fibres from the under- side of the leaves being taken. These are collected in water, scraped over the edge of a shell to free them from adhering cellular tissue and epidermis, and more than once washed in a running stream, followed by renewed scraping till the desired purity of fibre is attained. This native process is exceedingly wasteful, not more than one- fourth of the leaf-fibre being thereby utilized. But up till 1860 it was only native-prepared phormium that was known in the market, and it was on the material so carefully, but wastefully, selected that the reputation of the fibre was built up. The troubles with the Maoris at that period led the colonists to engage in the industry, and the sudden demand for all available fibres caused soon afterwards by the Civil War in America greatly stimulated their endea vours. Machinery was invented for disintegrating the leaves and freeing the fibre, and at the same time experi ments were made with the view of obtaining it by water- retting and by means of alkaline solutions and other chemical agencies. But the fibre produced by these rapid and economical means was very inferior in quality to the product of Maori handiwork, mainly because weak and un developed strands are, by machine preparation, unavoidably intermixed with the perfect fibres, which alone the Maoris select, and so the uniform quality and strength of the material are destroyed. No means have yet been devised for producing by mechanical or chemical means fibre in the perfect condition it shows when selected and prepared by Maoris. Phormium is a cream-coloured fibre with a fine silky gloss, capable of being spun and woven into many of the heavier textures for which flax is used, either alone or in combination with flax. It is, however, principally a cordage fibre, and in tensile strength it is second only to Manila hemp ; but it does not bear well the alternations of wet and dry to which ship -ropes are subject. It is largely used as an adulterant of Manila hemp in rope-making, and recently it has come into use as a suitable material for the bands of self-binding reaping-machines. Between 1864 and 1876 there were exported from New Zealand 26,434 tons of phormium, valued at 592,218; in 1881 the exports were 1307 tons, of the value of 26,285. PHOSPHORESCENCE, a name given to a variety of phenomena due to different causes, but all consisting in the emission of a pale more or less ill-defined light, not obviously due to combustion. The word was first used by physicists to describe the property possessed by many substances of themselves becoming luminous after ex posure to light. Such bodies were termed "phosphori," and the earliest known appears to have been barium sulphide, which was discovered by Vincenzo Cascariolo, a cobbler of Bologna, at the beginning of the 17th century. See PHOSPHORUS. Subsequently, when certain animals were observed to be similarly endowed, the word " phos phorescent " was applied to them also. It is clear, how ever, that the light derived from previous exposure to light, which thus becomes, as it were, stored up, is hardly comparable with that which is produced by living proto plasm and evidently under the control of the nervous system. It has been suggested that this latter should have a special name appropriated to it, and here it will certainly be convenient to divide the subject into two heads in accordance with this distinction. A. PHOSPHORESCENCE IN MINERALS. In addition to the phosphorescence after insolation already alluded to (see LIGHT, vol. xiv. p. 603) many minerals exhibit this property under other circumstances : (a) on heating to a temperature much below what is known as "red heat" (fluorspar, lepidolite, quinine) this being often attended with a change in molecular structure or in specific heat ; (I) on friction, as in the case of fused calcium chloride (Homberg s phosphorus) ; (c) on cleavage, a property mani fested by mica, the two split portions becoming electrified the one positive, the other negative ; (d) on crystallization, as boracic acid after fusion, or water on rapid freezing. 1 A few meteorological phenomena may here be mentioned. Rain has been seen to sparkle on striking the ground, and waterspouts and meteoric dust have presented a luminous appearance. The ignis fatuus, or will-o -the-wisp, seen in marshy districts, has given rise to much difference of opinion : Kirby and Spence suggest that it may be due to luminous insects ; but this explanation will certainly not apply in all cases, and it is perhaps on the whole more reasonable to believe that the phenomenon is caused by the slow combustion of marsh gas (methyl hydride). B. PHOSPHORESCENCE IN ORGANISMS. The vegetable kingdom has furnished few instances of the property under consideration ; the earliest on record took place in the year 1762, when a daughter of Linnaeus saw luminous emana tions from a species of Tropaeolum, since which time a like appearance has been noticed in Helianthus annum, Lilium bidbiferum, Calendula officinalis, Tagetes patula, and T. erecta, all of which are red or orange -coloured flowers. A few cryptogams have been seen to shine in the dark, e.y., Schistostega osmundacea among the liverworts ; Rhizo- morp/ia subterranea, Fungus igneus in Amboyna, and other fungi in Brazil and Italy ; and the mycelium (thread-like fibres) of other species growing in decayed wood is also occasionally luminous. There are also a number of small marine phosphorescent organisms ^(Pyrocystis, Peridinium], concerning which it is impossible to say with certainty whether they should be referred to the animal or the vege table kingdom. But the most brilliant as well as the most varied and interesting cases of phosphorescence belong to the animal world, and there is not one of the larger groups which does not furnish some instances of it. Nature of the Light. The light emitted by different animals varies very much in colour : green has been noticed in the glow-worm, fire -flies, some brittle -stars, centipedes, and annelids ; blue is seen in the Italian fire fly (Luciola italica) ; and this and light green are the pre dominant colours exhibited by marine animals, although the beautiful Girdle of Venus and some species of Salpa and Cleodora appear red, and Pavonaria and other gorgonoids lilac. The curious lantern-fly (Fulgora 2)y> orhynchus) has a purple light. One very remarkable instance is mentioned of an Appendicularia in which the same individual appeared first red, then blue, and finally green. 3 In comparatively few cases has the light been examined by the spectroscope. Panceri 4 states that in every instance observed by him it was monochromatic, the spectrum consisting of a continu ous band without any separate bright lines ; in Pholas this band extended from the line E of the solar spectrum to a little beyond F ; in Umbellula, examined on the voyage of the " Challenger," it was sharply included between the lines b and D. 5 Luminous Organs. In the lowest forms of life and in 1 Phipsou, Phosphorescence, London, 1862. 2 Ehrenberg, Das Leuchten des Meeres, 1835, and in Abhandl. k. Akad. Wiss., Berlin (1834), 1836. 3 Giglioli, "La Fosforescenza del Mare," in Bollet. d. Soc. Geog.- Geol. Ital, 1870. 4 Numerous papers in Atti Accad. Sci. Fis. e Mat., Naples, 1870- 78, and abstr. , Ann. Sci. Nat., ser. 5, vol. xvi. , 187 2. 5 Thomson, Voyage of the Challenger : the Atlantic, London, 1877, vol. i. p. 150.