Page:The New International Encyclopædia 1st ed. v. 04.djvu/817

CHRONOLOGY. 71 Spain. Portugal, Africa, ami parts of France, dated from the coiiciuesl of Spain by Auf;iistus in B.C. 3!l. .s the era of Spain liei,'an .laiuiary 1, 38, subtract .'SS from the number of the year to chaniie from the Si>anish era to the Christian. The followin'; table gives the precise dates of the beginning of the eras just mi'nlioned and of others of less importance: B.C. Grecian. Mundane September 1, 5598 Constantinople, Civil September 1. .to08 .Mexaudrian ....ug;ist 29. 5502 Antioch. Mundane September 1. nMi Julian Peri™! Jannar.v 1, -jaa Mundane, UBlier October 4ooi Mundane. Jewish October .J. .1 Abraham October 1, iuU Ol.vmpiads •'>•?; „V ill.' Kome, foundation of ...April i*. im Nnbona.ssar Febninr.v 2G, .4i Metonic C.vcle .....July ^>. ij- Macedonian, or Grecian September 1. ^li ■l',.|.](,„ October 1», l-'l> Kiiioiiiam!'.;!..: October IIU Cwsarian, ot AntiocU September 1, 48 Julian Year .lanuary 1. 45 Spanish Era anuary 1, 38 A^^iii,, January 1, JO AUfc-ust'anV.V.V.V. February 14, 2" Various other systems of ehronologr may be found mentioned under the names of the nations ■by whom they were employed. See also Calen- DAK; Ye.r; ^Ioxtii; Day; Cycle; etc. CHRONOM'ETEK ( Fr. chronomi-tre, It. crotioinctra. from Gk. xp6to5. cliroiios, time + li4Tpov, metrim, measure). The name given prin- cipally to such time-keepers as are used for de- termining the longitude at sea. The mechanism is essentially the same as that of a common watch, only the size is generally greater ; the balance-wheel is compensated for variations of temperature; and the wliole instrument is hung in a frame of balancing rings called gimbals. These prevent the shi])"s motion from influencing the iliii'iii'iiiiti'i '- late too much. CHRON ONHOT ONTHOL'OGOS ( fantasti- cally coined word). A burlesque by Henry Carey, produced February 22. 1734, at the Hay- market, and described as "the most tragical tragedy ever yet tragedized." It was partly suggested by Fielding's Tom Tluimb. The title character is the Monarch of Quecruinmania (q.v.), anU has become the type of all brag- garts. The play was published in the quarto edition of his dramatic works (Limdon, 1743). CHRON'OSCOPE (Fr. chronoscope. It. cro- iwscoiio, from Gk. xpii'ot, chronos. time -|- aKoirSs. skopos, watcher, from axopeiv, skoprin. to watch). .An instrument for measuring accurately small intervals of time, used in psychology, physiology. and in many departments of e.xjierimental and applied physics. The first attempt to measure a very small period of time was made by Sir Charles Wheatstone in 1.S34. when he endeavored to ascertain the duration of the electric spark. This was accomplished by means of a revolving mirror; and as this apparatus was the first and simplest of a number of similar instruments, it may be described at some length. On a hori- zontal axis capable of being revolved at high speed, a mirror was fixed. The rays issuing from a luminous point, such as a small flame, were reflected from the mirror when at rest, and reached the eye of the observer. If the mirror is slowly revolved, the image of the luminous jxiint will be either raised or lowered, and if the speed of rotation is increased, insteail of a succession it CHRONOSCOPE. of images there will be seen a continuous streak or band of light. If the given source of light be supplanted by an electric spark, and the mir- ror set in rotation, as long as the duration of the sjiark is less than is required by the mirror to reflect the rays across the field in the form of a band, then the spark will apjiear as a iioiiit; but, increasing the speed of the mirnu', a stage will be reached where the image will be jiroduced in the form of a bright streak. The time of the spark can then be calculated in the following way: First the velocity of the mirror is observed; then, suppose that the image of the spark ex- tends over what is equivalent to one-half a de- gree of arc. As the movement of the reflected ray is, from the laws of reflection, twice that of' the reflecting mirror, it would follow that ■when the mirror was revolving at a vehx'ity of SOO revolutions per second, the time consumed by the mirror in causing the spark to appear as a streak of light would be -g^ X i X tIiT X J or TTTJinnT "f ^ second. Wheatstone also employed this apparatus to .study the time consumed b}' an electric current in passing over a conductor, using for this pur- pose the sparks furnished at dift'erent lengths of the conductor, and measuring the ditVerence in time between their occurrences. A rotating mir- ror was also used by Feddersen in his researches on the electric spark, and again by Rood, the former employing a concave mirror, while the latter used a plane mirror in connection with a system of lenses. To Wheatstone is due another form of chrono- scope, which was used for measuring the veloc- ity of a projectile from the time it left a can- non until any desired point was reached. This apparatus in its essence consisted of a clock which was set in motion and stopped by the armature of an electromagnet. Across the muzzle of the gun a wire was placed which was broken at the exit of the projectile and the circuit opened, thus releasing the armature of the electro-magnet and setting in motion the clock- ■work. 'hen the shot reached the required dis- tance the circuit was closed, and the clock stopped in a similar fashion. Wheatstone did not claim a greater accuracy for this instrument than to Ti'j of a second, but improvements by Hipp, who, keeping the clockwork in motion, tised the magnets only to throw the indicating part of the apparatus into gear with the move- ment, made the instrument more servit^eablc. W. Siemens used a rapidly rot^iting cylinder, on a paper covering of which sparks from a cir- cuit containing Leyden jars made the record- marks. The introduction of a seconds pendulum into the circuit gave a record of the time by causing spark-punctures at regular intervals, and the desired times cotild be found by com- paring the distances. With this apparatus the velocity of a projectile while in the bore of the cannon could be measured, it lieing only neces- sary to insert insulated conductors at different points where the circuit could be made or broken by the traveling shot. Siemens also used this form of chronoscope, or chronograph, to measure the velocity of the electric current. Helmholtz improved the instrument by providing mecha- nism to giv(i a constantly increasing velocity, making his measurement when the desired rate of speed was reached, the regulation being elTect- (d bv the action of centrifugal force. This form