Page:The American Cyclopædia (1879) Volume I.djvu/96

 76 ACTINISM is that the liquids in our eyes cannot transmit waves of such great velocity ; when this velo- city is decreased by throwing the spectrum on some fluorescent substance, as paper, painted with a solution of quinine, or on uranium glass, the lines may be rendered visible. The so- called fluorescent substances reduce the ve- locity of the luminous waves falling on them ; in fact, they emit luminous waves of a less ve- locity than those by which they arc illuminated. Mr. Rutherfurd of New York has made the most elaborate photographs of all the lines in the actinic portion of the solar spectrum, the invisible as well as the visible, to the number of several thousand. A few of these lines are represented in the spectrum given here, of VI S I BLE LINES INVISIBLE LINES D E F GBIKX. G HIKL M N O P VIOLET. DARK SPACE. Prismatic Spectrum of Solar Light LUMINOUS RArS ACTINIC RAYS Curves representing 1 the comparative Intensity of the luminous and actinic rays in different parts of the solar spectrum. which only the portion from A to H is visible, while that from H to P is invisible, but may be photographed, even to a further extent than is here represented. The height of the un- shaded curve below represents the intensity of the light in the corresponding portion above, while the height of the shaded curve represents the intensity of the actinic action. It is seen that while the strongest light is in the yellow between the lines D and E, there is a total ab- sence of actinism here ; the strongest actinism is found near the lines H, where there is scarcely any light left, so that the spectrum dwindles down in darkness at that spot, while this ac- tinism extends about twice the length of the visible spectrum. In regard to the asserted action of the actinic rays on germination and the growth of plants, the most conscientious experiments have proved that only darkness promotes germination, and that plants want for their growth not that light alone from which the heated rays have been eliminated by pass- ing it through blue or violet glass. Such glass cannot increase the actinic power, but only de- crease the light and heat, and experience has shown that most plants suffer decidedly by such treatment ; that the green coloring matter of the leaves, of which the chlorophylline is the most important, needs the red rays for its pro- motion ; and that all plants must, in order to ACTION prosper, have the benefit of the full unadulte- rated solar light. ACTDfOMETER, the name generally but im- properly applied to a thermometer intended to measure the heat of the solar rays. The first so-called actinometer was made by Sir John Herschel in 1825, and consisted of a thermom- eter with a large bulb filled with the blue solution of the ammonia sulphate of copper, enclosed in a box with plate glass on top. When exposed to the sun's rays the expansion of the liquid indicates their intensity. The instrument is nearly identical in its results with that of Pouillet, which he calls pyrheli- ometer. Recently an ordinary mercurial ther- mometer enclosed in a box, and used alter- nately in the shade and in sunshine, was de- scribed by the Rev. Mr. Hodgkinson under the name of actinometer. A true actinometer is an instrument to measure the actinic or chemi- cal power of the solar rays. The first contri- vance to effect this object was the darkening of a surface sensitized by chloride of silver. The difficulty here was to make a preparation which was always uniformly sensitive. Dr. John W. Draper of New York discovered the important fact that of a mixture of equal vol- umes of chlorine and hydrogen, the amount combining to form chlorhydric acid is directly proportional to the actinic intensity of the light and the time of exposure. He made use of this property for the purpose of practical actinometry ; while recently Bunsen and Ros- coe have devised an actinometer based on the very same principle, and giving results of the most absolute scientific accuracy. There are, however, many other actions of this kind known in chemistry which may be more con- veniently employed. A solution of chloride of gold and oxalic acid will remain clear in the dark, while gold is precipitated by exposure to actinic rays, the amount of gold being propor- tional to the intensity of the rays and the time of exposure. See " Philosophical Transactions," 1859, p. 879; 1852, p. 139. ACTION, the formal demand of one's right from another in a court. In the Roman law action is defined to be either the right which one has of seeking in a judicial tribunal that which is his due, or the pursuit itself, or the exercise of the right. In our law the pursuit of the remedy is properly the action, and the right on which it rests is the cause of action. In its usual sense the word describes all the proceedings incident to the demand of the right, including the adjudication of the court upon it. As actions are appeals to the supreme power of the state, to decide upon the matters in controversy between the parties, they are, except where recent reforms hi procedure have changed the practice, commenced by writs is- sued out of courts, in the name of the sov- ereign, or of the judges as his representatives, calling upon the defendant to come into court and answer. Such writs still remain in many of the states and in most of the courts of the