COMET 



1510 



COMITIA 



ity, although it is so far from the earth that it 

 appears from day to day apparently stationary. 

 The name is derived from the Greek word 

 komctes, which literally means long-haired, in 

 reference to the beard or tail which usually 

 precedes or follows the comet. Few comets 

 are visible to the naked eye, though some have 

 tails many millions of miles in length. About 

 800 comets have been recorded, but there are 

 probably thousands that cannot be detected 

 by the most powerful instruments. Apparently, 

 comets consist of three parts the nucleus, or 

 bright, starlike portion; the coma, or mass of 

 matter surrounding it, and the tail. The three 

 parts are not always clearly defined, however, 

 and the comet may appear merely as a lumin- 

 ous haze. 



The tail is formed by a mass of gaseous mat- 

 ter scattered by the nucleus of the comet itself. 

 As it approaches the sun the tail is behind 

 the nucleus; as it travels away from the sun 

 the tail precedes it. In other words, the mat- 



Diagram showing how a comet's tail always 

 points from the sun. 



ter of which the tail is composed is repelled 

 instead of being attracted by the sun. It is 

 generally believed that comets are nebular 

 masses surrounding a nucleus, or center of 

 meteoric particles which in their course through 

 space have been captured by the attraction 

 of some planet, around which they then re- 

 volve. This revolution periodically brings them 

 under the attraction of the sun, causing them 

 to approach sufficiently near to become visible 

 from the earth. Thus, Neptune is known to 

 have a family of six captive comets, which will 

 revolve round that planet until captured by 

 some superior force. 



A comet may be visible for a week, a month 

 or even as long as two years. Sometimes the 

 approach to the sun is in the form of a parab- 

 ola (which see), from far beyond the solar 

 system. It may sweep in a mighty curve part 

 way round the sun, then branch away at an 

 angle, to disappear in space without ever 



again becoming visible. The last comet seen 

 without the aid of . a telescope was Halley's 

 comet, named after its discoverer. Halley an- 

 nounced in 1705 that this visitor would return 

 in 1759, 1835 and 1910, and his predictions were 

 fulfilled. 



In addition to Halley's cornet the most 

 important have been Lexell's, appearing in 

 1770 without being seen since; Biela's, which 

 in 1845 broke into two parts, and Enckes', 

 which returns at regular intervals of about 



THREE TYPES OF COMET TAILS 

 (a) Long, almost straight, and composed per- 

 haps of hydrogen; (ft) curved, supposed to be 

 hydrocarbon vapors; (c) short and stubby, prob- 

 ably metallic vapors of considerable density. 



three years. In 1858 the most remarkable of 

 all comets was discovered by Donati. It was 

 singularly bright and was watched by astron- 

 omers with great interest. 



It has always been customary among super- 

 stitious people to regard the appearance of a 

 comet as a portent of disaster. The appearance 

 of a comet in 1456 caused such terror that in 

 every Christian church in Europe the prayer, 

 "Lord save us from the Devil, the Turk and 

 the comet" was added to the service. Science 

 has so thoroughly explained the phenomenon, 

 however, that it is only the most ignorant who 

 regard such an appearance as otherwise than 

 natural. What would happen if the earth col- 

 lided with a comet's tail in its path would 

 probably be merely a dust storm, and nothing 

 in any way terrifying. F.ST.A. 



Related Subjects. The following articles in 

 these volumes contain information which will 

 be helpful to the reader interested in this topic : 

 Astronomy Nebula 



Halley, Edmund Parabola 



Meteor Star 



COMITIA, komish'iah, the legal meetings 

 of the ancient Romans, in which the people, 

 summoned by a magistrate, voted on ques- 

 tions relating to the state. They are thus to 

 be distinguished from the contiones, or mass 

 meetings. The oldest form of assembly was 

 the Comitia Curiata, or assembly by curiae 

 (wards), the members of which belonged to the 

 patrician, or favored, class. This assembly 

 made laws, determined upon peace and war and 

 elected the king. 



