390 



CON DOTTIER I CONE. 



wards the end of the middle ages, who sought for 

 service in every war, ami fought not for their coun- 

 try, hut for pay and plunder, and offered their assis- 

 tance to every party which could pay them. These 

 bands originated in the endless wars and fends of the 

 Italian Mates ami governments at that time, and the 

 vhole military power soon came into their hands. 

 They consisted principally of men too ignorant or too 

 indolent to obtain an honest livelihood, or who wish- 

 ed to escape the punishment of some crime. They 

 included, however, many people who had been de- 

 prived of their fortunes by these wars. As these 

 men had not the slightest interest in those who hired 

 them but that of being paid, and of finding opportu- 

 nities for plunder, wars terminated with very little 

 bloodshed, sometimes with none; for when the 

 bands of condottieri met, the smallest in number not 

 unfrequently surrendered to the other. The most 

 ambitious among them, however, had higher views. 

 Such was Francesco Sforza, who, being chosen by the 

 Milai.ese to command their army, made himself, in 

 1451, their duke and lord, and whose posterity con- 

 tinued to possess sovereign power. There is little 

 difference between most of the condittieri and some 

 of the nobler kind of robbers. See Captain, 



CONDUCTOR OF LIGHTNING is an instru- 

 ment, by means of which either the electricity of the 

 clouds, the cause of lightning, is conducted without 

 explosion, into the earth, or uie lightning itself is in- 

 tercepted and conducted, in a particular way, into the 

 rnrth or water, without injuring buildings, ships. &c. 

 This invention belongs to doctor Franklin. While 

 making experiments on electricity, he observed that 

 a pointed metallic wire, if brought near an electrified 

 body, gradually deprives the latter of its electricity 

 in such a manner that no sparks appear. Therefore, 

 as clouds are electrified, he thought that they might 

 be deprived of their electricity (which is the cause of 

 lightening and of its striking), if a pointed metallic 

 rod were fastened upon the highest part of a building, 

 and a wire carried down from this into the earth, so 

 that the electricity of the cloud, attracted by the 

 point, might be conducted into the ground. Frank- 

 lin's conjecture proved to be well founded, and con- 

 ductors were soon after introduced into many coun- 

 tries. They at first consisted of an iron rod, running 

 down the sides of a building into the earth, while its 

 point rose several feet above the building. Experi- 

 ence, thus far, shows the best construction of con- 

 ductors to be this : The conductor consists of a rod 

 of iron, an inch thick, to the upper end of which is 

 attached a tapering piece of copper, eight or nine 

 inches in length, gilded, to prevent its rusting. 1 his 

 rod is fixed to the highest part of a building, in such 

 a way as to rise at least five or six feet above it : to 

 this are fastened strips of copper, three or four inches 

 broad, and rivetted together, which must reach to 

 the earth, and be carried into it about a foot deep. 

 The strips are to be carefully nailed upon the roof 

 and against the wall of the building. The first con- 

 ductors in Europe were erected at Payneshill, in 

 England, by doctor Watson, in 1762, and upon the 

 steeple of St James' church, at Hamburg, in G ermany, 

 in 1769. In modern times, conductors have been 

 proposed to supersede those formerly in use. Among 

 them is the cheap one of Nicolai, made of strips of 

 tin, which has already been used ; for instance, at 

 Lohmen, near Pirna. 



CONDUIT (French), in architecture ; a long nar- 

 row passage between two walls, or under ground, 

 for secret communication between various apartments, 

 of which many are to be found in old buildings ; also 

 a canal of pipes, for the conveyance of water ; a sort 

 of subterrane'ous or concealed aqueduct. The con- 

 struction of conduits requires science and care. The 



ancient Romans excelled in them, nml formed UIP 

 lower parts, whereon the water r.n, \\itli cement of 

 Midi an excellent quality, that it has become as hard 

 as the stone itself, which it was employed to join. 

 There are conduits of Unman aqueducts still remain- 

 ing, of from five to six feet in height, and three tect 

 in width. Conduits in modern times, are generally 

 pipes of wood, lead, iron, or pottery, for conveying 

 the water from the main spring or reservoirs to the 

 different houses and places where it is required. 



CONE, in geometry; a solid figure having a circle 

 for its base, and its top terminated in a point, or ver- 

 tex. This definition, which is commonly given, is 

 not, in mathematical strictness, correct ; because no 

 circle, however small, can become a mathematical 

 point. But these deficiencies of mathematical strict- 

 ness connected with constructive geometry, which is 

 based on figures and diagrams, are avoided by analy- 

 tical geometry, which operates without figures. 



The figure might be called the round pyramid, ac- 

 cording to the definition of a pyramid. Cones are 

 either perpendicular, if the axis, that is, the line from 

 the vertex to the centre of the base, stands perpendicu- 

 larly on the base ; or oblique, or scnle?ious, if the axis 

 does not form a right angle with the base. (1) if a 

 cone be cut perpendicularly to the base, the section is 

 a triangle ; (2) if a cone is cut parallel with its base, 

 the section is a circle ; (3) if the section is made ol>- 

 liquely, that is, nearer to the base at one end th;;n at 

 the other, a curve is obtained,which is called an ellipse; 



(4) if the section be made parallel with the axis, per- 

 pendicularly from the vertex, or so as to make a 

 greater angle with the base than is made by the side of 

 the cone, the curve obtained is called a hyperbola ; 



(5) if the section be made parallel with one side 

 of the cone, in such case the curve is called a 

 parabola. These three lines, figures, and planes are 

 called conic sections, and form one of the most import- 

 ant parts of mathematics, which is distinguished for 

 elegance, demonstrating, with surprising simplicity 

 ana beauty, and in the most harmonious connexion, 

 the different laws, according to which the Creator has 

 made worlds to revolve, and the light to be received 

 and reflected, as well as the ball thrown into the air 

 by the playful boy, to describe its line, until it falls 

 again to the earth. Few branches of mathematics 

 delight a youthful mind so much as conic sections ; 

 and the emotion which the pupil manifests, when they 

 unfold to him the great laws of the universe, might 

 be called natural piety. Considering conic sections 

 as opening the mind to the true grandeur and beauty 

 of the mathematical world, whilst all the preceding 

 study only teaches the alphabet of die science, we 

 are of opinion that the study of them might be ad- 

 vantageously extended beyond the walls of colleges, 

 into the higher seminaries for the education of fe- 

 males. The Greeks investigated the properties of 

 the conic sections with admirable acuteness. A 

 work on them is still extant, written by Apollonius 

 of Perge. The English have done a great deal in- 

 wards perfecting the theory of them. In teaching 

 conic sections to young people, the descriptive me- 

 thod (resting on diagrams) ought always to be con- 

 nected with the analytic method. 



