CIS 



C1T 



Bordered with a parapet, thrown up 

 quite round the beseiger's camp, by way 

 of security against any army that may 

 attempt to relieve the place, as well as 

 to prevent desertion. See FORTIFICA- 

 TION. 



CIRRUS, in botany, a clasper or ten- 

 dril- that fine spiral string or fibre, put 

 out from the foot-stalks, by which some 

 plants, as the ivy and vine, fasten them- 

 selves to walls, pales, or trees, for sup- 

 port. It is ranked by Linnxus among the 

 fulcra, or parts of plants that serve for 

 support, protection and defence. Tendrils 

 are sometimes placed opposite to the 

 leaves, as in the vine ; sometimes at the 

 side of the foot-stalk of the leaf, as in the 

 passion-flower ; and sometimes, as in the 

 winged-pea, they are emitted from the 

 leaves themselves. 



CIRSOCELE, or hernia varicos a, in sur- 

 gery, a preternatural distension or diva- 

 rication of the spermatic veins in the pro- 

 cess of the peritonaeum. 



CISSAMPELOS, in botany, a genus of 

 the Dioecia Monadelphia class and order. 

 Natural order of Sarmentacex. Menis- 

 pernia, Jussieu. Essential character : 

 male, calyx four-leaved ; corolla none ; 

 nectary wheel-shaped ; stamina four, with 

 cornate filaments. Female, calyx one- 

 leafed, ligulate, roundish ; corolla none ; 

 styles three ; berry one-seeded. There 

 are three species. 



CISSOID, in geometry, a curve of 

 the second order, first invented by 

 Diocles, whence it is called the cissoid of 

 Diocles. 



Sir Isaac Newton, in his appendix 

 "De -Equationum Construetionelineari," 

 gives the following elegant description of 

 this curve, and at the same time shews 

 how, by means of it, to find two mean 

 proportionals, and the roots of a cubic 

 equation, without any previous reduc- 

 tion. Let AG (Plate III. Miscel. fig. 

 12) be the diameter, and F the centre of 

 the circle belonging to the cissoid ; and 

 from F draw F D, F P, at right angles to 

 each other, and let F P be = A G ; then 

 if the square P E D be so moved that one 

 side E P always passes through the point 

 P, and the end D of the other side E D 

 slides along the right line F D, the middle 

 point C of the side E D will describe 

 one leg G C of the cissoid ; and by con- 

 tinuing out FD on the other side F, 

 and turning the square about by a 

 like operation, the other leg may be de- 

 scribed. 



This curve may likewise be generated 

 by points in the following manner : 



Draw the indefinite right line B C 

 (fig. 13.) at right angles to A B the 

 diameter of the semicircle A O B, and 

 draw the right lines AH, AF, A C, &c 

 then if you take A M = L H, A O = 

 OF, Z C = A N, &c. the points M, O, 

 Z, &c. will form the curve A M O Z of 

 the cissoid. 



CISSOID, properties of the .- it follows 

 from genesis, that drawing the right 

 lines PM, KL, perpendicular to AB, 

 the lines A K, P N, A P, P M, as also 

 A P, P N, A K, K L, are continual propor- 

 tions, and therefore that A K = P B, 

 and P N = I K. ' After the same manner 

 it appears that the cissoid AM O bisects 

 the semicircle A O B. Sir Isaac New- 

 ton, in his last letter to Mr. Leibnitz, 

 has shewn how to find a right line equal 

 to one of the legs of this curve by means 

 of the hyperbola ; but suppressed the in- 

 vestigation, which, however, may be 

 seen in his fluxions. The cissoidal space 

 contained under the diameter A B, the 

 asymptote B C, and the curve A O Z of 

 the cissoid, is triple that of the generat- 

 ing circle A O B. 



CISSUS, in botany, a genus of the Te- 

 trandria Monogynia class and order. Na- 

 tural order of Hederacese. Vites, Jus- . 

 sieu. Essential character: berry one- 

 seeded, surrounded by the calyx, and 

 four-parted corolla. There are fifteen 

 species ; natives of both Indies. 



CISTUS, in botany, rock rose, or gum 

 cistus, a genus of the Polyandria Mono- 

 gynia class and order. Natural order of 

 Rotaceae. Cisti, Jussieu. Essential cha- 

 racter : corolla five-petalled ; calyx five- 

 leaved, with two of the leaflets smaller; 

 capsule. There are sixty-six species, all 

 of which are great ornaments to a gar- 

 den ; their flowers, though of short du- 

 ration, are succeeded by fresh ones al- 

 most every day for about two months 

 successively ; the flowers are the size of 

 a middling rose, but single, and of various 

 colours ; the plants continue their leaves 

 all the year; they are most of them hardy 

 enouch to live in the open air all the win- 

 ter, except in very severe ones, which 

 often destroy many of them ; so that a 

 plant or two of each sort should be 

 kept in pots, and sheltered, to preserve 

 the kinds. They are natives of warm cli- 

 mates. 



CITADEL, a place fortified with four, 

 five, or six bastions, built on a convenient 

 ground near a city, that it may command 

 it in case of a rebellion. The city there- 

 fore is not fortified on the part opposite 

 to the citadel, though the citadel is 



