Page:The New International Encyclopædia 1st ed. v. 16.djvu/659

* PYRENEES. 575 PYRHELIOMETER. PYRENEES, Hautes. A southwestern fron- tier di'iJiirtment of France. See Hautes-Py- Bli-X^ES. PYRENEES, Peace of the. A treaty of- peace concluded between France and Spain, No- vember 7, 1059, on an island in the Bidassoa River. It brought to an end the struggle be- tween the two powers, -which with intervals of peace had continued since the beginning of the sixteenth century, when Louis XII. of France and Ferdinand the Catholic entered into the contest for supremacy in Italy. Spain ceded to France most of Artois, and parts of Flander.s, Hainault, and Luxemburg; in the south it sur- rendered Roussillon and a part of Cerdagne, thus making the Pyrenees the boundaries be- tween the two countries. The Infanta ilaria Theresa was promised in marriage to the young Louis XIV. ( (|.v. ) . PYRENEES-ORIENTALES, pe'ra'na' zo're- aN'tal'. A southern maritime department of France (q.v.), bounded on the east by the Jlediterranean, and on the south by the Pyrenees (ilap: France, .J 9). Area. 1592 square miles. The department presents a series of three parallel valleys formed by spurs from the Pyrenees, which run east and west, and are watered by the Agly, the Tet (the principal river), and the Tech. The southwest corner is drained by the S6gre ( Segura ), a tributary of the Ebro. An extensive plain oc- cupies all the north and east of the department. The climate is equable. The vegetable products include fine grain and some of the choicest fruits. Wines constitute the wealth of the district, and include the red wines of Roussillon and the white muscatel of Rivesaltes. The chief exports are wine, cocoons, live stock, and animal products, anchovies, etc. Capital, Perpignan (q.v.). Popu- lation, in 1890, 208,387: in 190l, 212,121. Consult Companyo, Histoire natureUe du depnrfement des Pi/rinees-Orientates (Perpignan, 1802-04). PYRENOID (from Gk. irvp-^v, iii/rCn, stone of a fruit + eUos, eidos, form). A differentiated portion of a chromoplast (q.v.) of proteid na- ture, which, since starch grains are usually formed around it. is sometimes called an amylum body. It is regarded as a food reserve. PYRETHRUM, pir'eth-rum. See IxsECT Powder and Colored Plate of Chby.s.^xthemums. PYR'GOS. A town of Greece, capita! of the Xomarchy of Elis. It is situated near the west coast of the !Morea, 40 miles southwest of Patras, in a fertile region producing great quantities of currants, grapes, and orange.s (Jlap: Greece, C 4 ). These products are exported through the port of Katakolon, with which the toAvn is con- nected by a short railroad. Railroads also run to Patras and to the ruins of Olvmpia. Popula- tion, in 1896. 12.708. PYRHELIOM'ETER (from Gk. np, pi/r, fire -f- ijXios, hflios. sun -|- y-irpov, mctron. meas- ure). The name given by Pouillet to an instru- ment devised by him for the purpose of measur- ing the amount of heat received from the sun in a tinit of time by a tinit surface. This quantity is sometimes called the 'solar thermal constant.' and all apparatus expressly designed to measure the intensitv of radiant heat may properlv be called pyrheliometers ; but, owing to the progress in our views with regard to the effects of solar radiation, it is not now generally recognized that the latter may produce either thermal, optical, or chemical effects, according to the nature of the substance upon which it falls, so that the pyrhc- liometer is really a special form of actinometer (q.v.) or radiometer. Pouillet's instrument, de- vised in 1837, "consists of a thermometer whose biilb is inclosed in a thin flat metallic box filled with water. The upper surface of the bo.x care- fully blackened is placed perpendicularly to the rays of the sun. The heating of the thermometer during five minutes' exposure to the solar action is noted, and also its cooling during five minutes when the sunlight is cut off by a screen. The elevation of temperature produced by the heat of the sun in five minutes, corrected for the effect of cooling or warming when the sun's rays are cut oft", is to be divided by the mass of the water in the apparatus and the area of the surface; this gives the quantity of heat expressed in calories as received by a unit surface in a unit time," In 1885 Professor Knut Angstrom de- vised his differential pyrheliometer, composed of two identical disks of copper, each carrying a thermo-electric junction and exposed alternately to the action of the sun, a galvanometer placed in the circuit of the two junctions measuring their difference of temperature; and in 1893 he brought out his compensating pyrheliometer. "Two thin strips of blackened metal identical in every way are placed side by side. One of these is exposed to the rays of the sun, while the other is kept in the shade; the latter is warmed up by an electric current until its temperature is identical with that of the strip that is warmert by the sunshine. This exact equality is shown by the fact that at this moment no thermal electric current passes between the two strips. Therefore at this moment the thermal effect of the solar radiation per unit of time is equal to that of the electric current. The intensity of the latter can easily be measured, and from it is calculated the absolute intensity of the solar radiation. A complete observation consists in making each of the two blackened strips become successively the exposed and the unexposed cal- orimetric body." In 1893 Chwolson constructed a pyrheliometer consisting essentially of two thin plates gilded on the back and blackened in front, alternately exposed to and shielded from sunshine, and whose differences of temperature can be measured many times in rapid succession by thermo-electric methods. Chwolson's ap- paratus has been adopted by the Russian meteorological service, while Angstrom's appara- tus has commended itself to the Weather Bureau of the L'nited States. Crova's mercury pyrhe- liometer consists of a mercurial thermometer bulb carefully blackened and receiving the solar rays through a narrow aperture of known area. The bulb is alternately shaded and exposed several times in sticcession and the differences be- tween the readings give the correct effect of th< sunshine. When the bulb has been properly cali- brated and its water equivalent is known, its changes of temperature can be converted into calories and the instrument becomes an absolute actinometer. The results of the best work that has been done with pyrheliometers give for the value of the solar thermal constant at the mean distance of the earth from the sun 4,0 calories per minute per square centimeter, but in general all such figures are affected by our ignorance of the absorption by the earth's atmosphere. A