SER 



SES 



their interior into irregular masses. 

 From these septaria is manufactured the 

 material for building under water, known 

 as Parker's or Roman cement. 



SEPTICl'DAL {septum, a division, 

 aedo, to cut). That kind of dehiscence 

 of fruits, in which the septa separate 

 each into two laminae, as in rhododen- 

 dron. Formerly, botanists used to say 

 that in this sort of dehiscence the valves 

 were alternate with the dissepiments, or 

 that the valves had their margins turned 

 inwards. 



SEPTI'FRAGAL {septum, a division, 

 frango, to break). That kind of de- 

 hiscence of fruits, in which the backs of 

 the carpels separate from the septa, 

 which adhere to the axis, as in convol- 

 vulus. 



SERIES. In Mathematics, a series is a 

 set of terms, finite or infinite in number, 

 connected together by addition or sub- 

 traction, and formed upon some distinct 

 law. An arithmetical series is one in 

 which each term differs from the preced- 

 ing by the addition or subtraction of a 

 constant number or quantity; a geome- 

 trical series is one in which each term is 

 a multiple of the preceding by a con- 

 stant factor. 



1. Series, infinite. A series of terms 

 proceeding according to some law, and 

 continued without limit. The sum of an 

 infinite series is the limit to which we 

 approach more nearly by adding more 

 terms, but which cannot be exceeded by 

 adding any number of terms whatever. 



2. A convergent series is one which has 

 a sum or limit, as above defined ; a di- 

 vergent series is one which has no such 

 sum or limit. Hence, every infinite 

 series in Geometrical progression, in 

 which the common ratio is less than 1, 

 is convergent. 



3. Series, recurring. If each succeed- 

 ing term of a decreasing infinite series 

 bear an invariable relation to a certain 

 number of the preceding terms, the 

 series is called a Recurring Series, and 

 its sum may be found. Thus a ■{■ {a + \) 

 ar -I- (2 a -H 2) a;2 -f (3a -f 3)a;3 + (5a-{-5) 

 x2 -f . . . is a recurring series, the co- 

 efficient of each term being the sum of 

 the co-efl5cients of the two preceding 

 terms. 



4. An exponential series is one whose 

 terms depend on exponential quantities ; 

 a logarithmic series is one whose terms 

 depend on logarithms ; and a circular 

 series, one whose terms depend on cir- 

 cular functions, as sines, co- sines, &c. 



301 



5. The general term of a series is a 

 function of some indeterminate quan- 

 tity X, which, on substituting succes- 

 sively the numbers 1, 2, 3, &c., for x, 

 produces the terms of the series. 



SERPENS. A northern constellation, 

 consisting of sixty-four stars. Mytho- 

 logically, it is the serpent carried by Ser- 

 pentarius, the serpent-bearer. 



SERPENTARIUS. Ophiuchus. A 

 northern constellation, containing se- 

 venty-four stars, the principal of which 

 is Ras Aliagus. 



SER'PENTINE. A rock of the pri- 

 mary series, closely related to diallage 

 rock, of irregular form and of various 

 colours : when opaque, it is named com- 

 mon serpentine ; when translucent, 

 noble or precious serpentine. It con- 

 sists of hydrate of magnesia with sub- 

 silicate of magnesia. The name is de- 

 rived from its frequent contrasts of 

 colour, like those of the skin of some 

 serpents. 



SERPU'LEANS. A family of cepha- 

 lobranchiate annellides, inhabiting cylin- 

 drical and tortuous calcareous tubes; 

 generally parasitic on shells. 



SERRICORNES {serra, a saw, cornu, 

 a horn). A family of the pentamerous 

 coleoptera, distinguished by the serrated 

 or toothed form of the antennae. They 

 have four palpi, and the body is com- 

 pletely covered by the elytra, or wing- 

 cases. 



SE'RTULUM. A term applied by 

 some botanists to the simple umbel, the 

 latter term being by them restricted to 

 the compound form of this inflorescence. 



SESQUI- (contracted from semisque, 

 and a half). A prefix to certain words, 

 denoting so much and half so much, the 

 whole of a thing and a half more. It is 

 used in chemical language when the ele- 

 ments of an oxide are as 1 to IJ, or as 

 2 to 3. The sulphurets, carburets, &c., 

 of the same substance are similarly de- 

 signated. Hence, also, the word sescu- 

 plum (quasi sesquiplum, from sesqui and 

 plica, a fold) ; thus ses cup lo-carhuietf 

 one and a half-fold carburet. 



Sesqui'duplicate. A term sometimes 

 found in treatises on Geometry, signifying 

 the ratio in which the greater term is 

 twice and a half times the less ; as the 

 ratio of 10 to 4; of 15 to 6 ; &c. 



SESSILE {sessilis, sitting). Destitute 

 of any support or peduncle, as a leaf 

 which has no stalk, or the shell of the 

 anomia. The term Sessiles has been 

 adopted for a division of the Cirrhopoda, 



