COM 



COM 



takes place in the combination of oxygen, 

 but, in a few cases, in that of chlorine 

 and of sulphur. Bodies which are con- 

 sidered as the causes of this phenomenon 

 are called supporters of combustion^ whilst 

 the radicals which combine with them 

 are called combustibles. 



1. Combustion, Invisible. A term ap- 

 plied by Davy to those phenomena of 

 combustion which are effected without 

 the disengagement of light, as when 

 oxygen and hydrogen, confined in tubes, 

 are carefully exposed to a high tempe- 

 rature. 



2. Combustion, Spontaneous. This is 

 said to occur in the human body ; and it 

 does occur when masses of vegetables, as 

 damp hay, or oily cotton, are heaped to- 

 gether. There are also cases on record 

 of the spontaneous ignition of charcoal, 

 both dry and moist. 



COxME'NIC ACID. A bibasic acid, 

 formed from the meconic acid, of which 

 it is a congener. It is decomposed by 

 heat, and another congener is produced, 

 viz. pyromeconic acid. 



CO'MET {KOfxijrr]^, from ko/jlti, hair). 

 Literally, a hairy star. A celestial body 

 which occasionally traverses our system 

 in a very eccentric orbit, without appear- 

 ing to form a part of it. Its central 

 point, which is more or less lustrous, is 

 called its nucleus. The nebulous light 

 surrounding the nucleus, is the chevelure 

 or hair. The luminous train by which 

 most comets are accompanied was for- 

 merly called beard or tail, accordingly as 

 it preceded or followed the comet in its 

 course. At present it is called tail, what- 

 ever be its position. Lastly, the nucleus 

 and the chevelure together constitute 

 the head of the comet. 



COMET A'RIUM. A machine show- 

 ing the motion of a comet about the 

 sun ; any instrument capable of describ- 

 ing an elongated ellipse. 



COMMA {KdfxfjLa, that which is struck). 

 The smallest interval in music, being the 

 ninth part of a major tone. 



COMMISSU'RAL {committo, to solder). 

 Belonging to a line or part by which 

 other parts are connected together. The 

 connecting line is the commissure. 



COMMON MEASURE. In Arith- 

 metic, a number which divides two or 

 more other numbers without leaving a 

 remainder. 



COMMON TERM. A logical expres- 

 sion for a term which is applicable in the 

 same sense to more than one individual 

 object. Common terms, therefore, are 



called "predicables," that is, affirmatively 

 predicable, from their capability of being 

 affirmed of others. See Singular Term. 



CO'MMUTATOR or GY'ROTROPE. 

 An apparatus included in the circuit 

 between the battery and the electro- 

 magnetic apparatus, for the purpose of 

 reversing the direction of the current 

 without the necessity of changing the 

 arrangement of the conductors from the 

 poles. 



COMPASS, MARINER'S. A mag- 

 netic needle, balanced on a pivot, for 

 pointing out the true direction of north 

 and south. In the mariner's compass, 

 the circle traversed by the point of the 

 needle is marked off into 32 rhumbs or 

 points; in the azimuth compass the same 

 circle is divided into 360°. 



COMPA'TIBLE TERMS. In Logic, 

 terms expressive of two views which 

 may be taken of the same object at the 

 same time, as to be "white and cold." 

 See Opposite terms. 



COMPENSATION PENDULUM. A 

 pendulum made of different substances, 

 so combined that the effects of* heat 

 counteract each other, and the length of 

 the rod remains unaltered. 



CO'MPLEMENT {compleo, to fill up). 

 A magnitude which, taken with another, 

 makes up a given magnitude. The com- 

 plement of an arc or angle is what is 

 required to complete a quadrant or right 

 angle. The arithmetical complement of 

 a number is the number by which it falls 

 short of the next higher decimal denomi- 

 nation. The complement of a logarithm 

 is the number by which a logarithm falls 

 short of 10. The complement of altitude 

 is the zenith distance ; that of latitude, 

 the poiat3tistance* ''-'■ " " ,{ ^ 



COMPOSITvE. The Synantherous 

 tribe of dicotyledonous plants. Herba- 

 ceous plants or shrubs with leaves alter- 

 nate or opposite ; flowers (called florets) 

 unisexual or hermaphrodite, collected in 

 dense heads upon a common receptacle, 

 surrounded by an involucrum ; florets 

 monopetalous ; anthers syngenesious ; 

 ovarium one-celled ; fruit a dry, inde- 

 hiscent pericarp, termed achenium or 

 cypsela. 



COMPOSITION {compono, to put 

 together). A technical term used by 

 geometers to signify one of the ways of 

 changing the order or magnitude of pro- 

 portionals, so that they continue still to 

 be proportionals. Thus of four propor- 

 tionals, the first, together with the 

 second, is to the s( cond, as the third, 



