Page:The American Cyclopædia (1879) Volume IV.djvu/618

 606 CIRCENSIAN GAMES CIRCULATION this time seems to have declined, and to have become gradually insignificant. It was subse- quently, under the later republic and the em- pire, a favorite place of retirement for wealthy Romans, having a peculiar attraction in the abundance and excellence of its oysters. It was sometimes selected as a place of exile, and the triumvir Lepidus was banished hither. Its ruins are still to be seen on the Monte della Cittadella, about 2 m. from the sea. The re- mains of its walls, constructed of polygonal blocks, show a massive style of architecture. C1RCENSIAN GAMES, the various combats and , contests exhibited in the Roman circus, said to have been first instituted by Romulus for the purpose of attracting the Sabines to his new town. A part of them were abolished by Constantino, others by the Goths ; but the chariot races continued at Constantinople till the siege of that city by the Venetians in 1204. CIRCLE, a plane figure bounded by a line every part of which is equally distant from its centre. This line is called the circumference, and in popular language the word circle is sometimes used for circumference. The diam- eter of a circle is a straight line which passes through its centre and is terminated at both ends by the circumference. The ratio of the diameter to the circumference was shown by Archimedes to be about as 7 to 22, and by Metius as still more nearly 113 to 855, which, though slightly too small, is as accurate as is needed for practical use. The exact ratio cannot be expressed in numbers, although many algebraic expressions can be obtained for it, of which we will give but one. If the number 4 be divided by 1, 6, 9, 13, and every 4th number in succession, and afterward by 8, 7, 11, and every 4th number in succession, the difference between the sum of the first set of quotients and that of the second set will be equal to this ratio ; or approximately in deci- mals, 3-14159265. The ratio of 7 to 22, decimally expressed, is 3'14285714; that of 113 to 355 is 3-14159292. CIRCLEYILLE, a city, capital of Pickaway co., Ohio, on the left bank of the Scioto river, and on the Ohio canal, which here crosses the river by a handsome aqueduct, 25 m. S. of Colum- bus; pop. in 1870, 5,407. It occupies the site of an aboriginal fortification of circular form, from which its name is derived. The sur- rounding country is rich and highly cultivated. The Cincinnati and Muskingum Valley railroad passes through it. It contains numerous mills and factories, and three weekly newspapers. There are 18 schools, of which 2 are high schools, 19 teachers, and 728 male and 688 female pupils in attendance. CIRCUITS (Lat. circiiitu, from circumire, to go around), the periodical progress of the sev- eral judges of the superior courts of the common law in England and Wales through the several counties for the purpose of administering jus- tice. The term is also applied to the several divisions of the kingdom which are made for ; the purposes of these visits, and through each of which one of the judges will go in order to hold courts twice or more each year in every county. The United States is also divided into circuits similarly, and the justices of the su- preme court and circuit judges go upon the cir- cuits periodically in like manner. There are like divisions of the several states for judicial purposes, and in some these are called circuits, in others not. (See COURT.) CIRCULAR MEASURE, a measure of angles produced by dividing the circumference of a circle, with its centre at the vertex of the an- gle, into 360 equal parts called degrees. Each degree is also divided into 60 minutes, and each minute into 60 seconds. Circular minutes and seconds are marked by accents ( ' and " ), while measures of time of the same name are marked m. and s. CIRCULATING MEDIUM. See MONEY. CIRCULATION. Under this title we shall examine only the circulation of blood in the animal economy, omitting all that relates to the circulation of lymph and chyle, and to the circulation of the nutritive fluids in plants. Be- fore stating by what decisive experiments and reasonings the eminent William Harvey (1619, 1628) proved the circulation of the blood, we must remind the reader of some points in the anatomy of man and of the higher animals which are essential to the understanding of our subject. The heart, which is at least one of the principal organs that circulate the blood, is a complicated muscular apparatus, composed of walls separating four cavities, two on the left and two on the right of the organ. Al- though there is only a muscular wall between these two sets of cavities, and although they be- long to one single organ or apparatus, the two sides of the heart, in which are these two sets of cavities, are sometimes called, for the sake of brevity, the right heart and the left heart. Of the four cavities of the heart and of their walls, two, the upper ones, are called the auri- cles, while the two lower ones are called the ventricles ; so that there is a left auricle and a left ventricle, constituting the left heart, and a right auricle and a right ventricle, constituting the right heart. The circulation of the blood takes place in the following way : From all the parts of the body black blood, called also venous blood because it comes by the veins, reaches the right auricle, which propels it into the right ventricle, from which it is sent to the organs of respiration, i. ., the lungs. The blood vessel that brings the blood from the right ventricle into the lungs is the pulmonary artery. The lungs send back this blood to the heart through blood vessels which, on account of their structural resemblance to veins, al- though they do not carry black or venous blood, are called pulmonary veins. In the lungs the blood by the influence of respiration becomes red, and in consequence the heart re- ceives red blood from the pulmonary veins. The left auricle is the place of reception for