Page:The New International Encyclopædia 1st ed. v. 01.djvu/132

in the large size of the individuals, which rarely form a colony. See Anthozoa and Sea-Anemone.

FIG. 1. FIG. 2. ACTINIARIA.

1. Vertical aspect of an Actiniaran, showing mouth and tentacles. 2. Sectional view: a, simple digestive sac; b, structure of the body-wall, showing septa.

ACTIN'OGRAPH (Gk. ἀκτίς, aktis, ray + γράφειν, graphein, to write). An instrument for recording automatically the chemical effects of radiations from any source, especially the sun. Formerly the actinic or chemical, the visual or optic, and the thermal or heat rays were spoken of as the components of a beam of sunshine as though all kinds of rays were bound up therein. But we now know that the sun radiates an immense variety of so-called waves or rays of different wave-lengths and that apparently any one of these waves may produce chemical, visual, or thermal effects, and perhaps electrical, depending upon the molecular nature of the object that it strikes. Thus the same wave that produces a special blue light in the solar spectrum will produce a little heat if it fall upon a delicate thermometer, or a great effect resulting in intense heat and light if it fall upon a proper mixture of chlorine and hydrogen or other chemicals. It is no longer proper to speak of the sun's actinic rays, but of actinic effects of the solar radiation. The simplest forms of actinograph are those that expose standard photographic plates or films (iodides, chlorides, or bromides of silver) to the sun's action for short, definite periods of time. Those that utilize the action of sunshine to cause the union of chlorine and hydrogen (Draper's and Bunsen's), or the precipitation of gold from a solution of the chloride of gold and oxalic acid, or the evolution of oxalic acid from a solution of ferric-oxalate and chloride of iron require complex measuring arrangements that do not easily lend themselves to graphic self-registration.

ACTIN'OLITE (Gk. ἀκτίς, aktis, ray + λίθος, lithos, stone). A calcium-magnesium-iron amphibole (q.v.) that includes the varieties nephrite, asbestos (q.v.), smaragdite, and uralite. Actinolite varies in color from a bright green to a grayish green, and usually occurs in the form of long, slender crystals in metamorphic rocks, commonly in talc.

ACTINOLITE-SCHIST, or Grünerite-schist. A rock with a banded or foliated structure, which contains a considerable quantity of actinolite. Commonly the actinolite lies in single crystals or in sheaf-like aggregates in a fine grained ground-mass of quartz or of quartz and feldspar, and its common associate is iron oxide, particularly in the form of magnetite, although many other minerals may be present in smaller quantities. The actinolite-schists are common alteration products, under deep-seated conditions, of iron carbonate or ferrous silicate rocks, particularly in the vicinity of igneous masses. The famous iron-bearing formations of the Lake Superior country were originally mainly iron carbonate or ferrous silicate, and, by their alteration, have yielded iron ore on the one hand and actinolite- or grünerite-schists on the other. The term "schist" as applied to these rocks is frequently a misnomer. Schists show a parallel dimensional arrangement of their constituents, but commonly the actinolite crystals in so-called actinolite-schists show but a slight degree, if any, of parallelism. The parallel structure is really a more or less faint banding due to the segregation of different kinds of minerals into layers. See Schistocity.

AC'TINOM'ETER (Gk. ἀκτίς, aktis, ray + μέτρον (Greek characters), metron, measure) . An instrument for measuring the effect of the sun's rays in producing chemical, i.e., actinic effects. As originally devised by Sir John Herschel, this title was applied by him to a thermometer whose bulb was filled with a blue solution of ammonia and sulphate of copper; the expansion of this solution by absorbing the sun's rays was supposed to measure the quantity of blue light or chemical rays in the beam of sunshine. At the present time it is known that actinometers, properly so called, measure only the effects of the energy transmitted to us in specific portions of the solar spectrum. In some arrangements this energy is all turned into heat and measured by its expansion effect. In other forms of apparatus it does molecular work of a chemical nature and is measured by these effects, as when a mixture of chlorine and hydrogen is converted into hydrochloric acid and the quantity of acid that is formed in years of time is the measure of the intensity. This includes the basis of the methods of Draper and Bunsen and Roscoe. When a mixture of ferric-oxalate and chloride of iron dissolved in water is exposed to sunshine it gives out carbonic acid gas; this is the basis of Marchand's apparatus. A photographic plate exposed for a short time receives an impression whose intensity may be measured on a scale of tints or shades and made the basis of a determination of the intensity of the sunshine. This method has been worked out by Bigelow and others. In general any apparatus for measuring the chemical effects of radiation from any source constitutes an actinometer properly so called, but the name is often improperly applied to apparatus that measures the total heating effect, as was the case in Herschel's apparatus; it is even now applied to the Arago-Davy and the Chwolson apparatus, all of which are, properly speaking, forms of pyrheliometer, and will be found described under that head.

AC'TINOM'ETRY. The general subject of the measurement of either the relative or the absolute effect of sunshine or other radiation either by visual, thermal, or chemical methods. This term is now being replaced by the more proper word radiometry.

AC'TINOMOR'PHY (Gk. ἀκτίς, aktis, ray + μορφή, morphē, form, shape). In botany, a term of symmetry used chiefly in connection with flowers. In an actinomorphic flower the members of each set are similar and arranged about a common centre, as are the parts of a radiate animal. If there are five petals, they are alike and are evenly distributed about the centre of