TORTOISK-SHELL. 



TORTURE. 



HI 



consequently the angle of tonion was 98f ( = 720' -21j). 

 Obtaining in like manner Mvenl other angles of torsion with the 

 corresponding-deviation* of the magnetic needle, and comparing them 

 together. Coulomb found that the force* of tonion are constantly 

 proportional to the sines of the deviations of the needle. 



In order to discover the law of magnetic action with respect to the 

 distance* between the attracting or repelling bodies, Coulomb placed a 

 magnetised needle in the stirrup of the balance, and after twisting tin- 

 wire by turning the micrometer stem at I on iU axis through a certain 

 number of degrees, he observed where the needle retted between the 

 opposing forces of tonion and the horizontal component of terrestrial 

 magnetism : assuming then that the deviations of the needle were 

 proportional to the forces of tonion, be found that, in order to make 

 the needle deviate one degree, it was necessary to employ a force of 

 torsion expressed by 35. The wire being then untwisted, and the 

 magnetised needle placed in the magnetic meridian, Coulomb intro- 

 duced in the glass case, in a vertical position, and also in the plane of 

 the magnetic meridian, a magnetised needle of the same dimensions as 

 the other, so that if the two needles could hare approached each other 

 they would have been in contact at about an inch from the extremity 

 of each ; but the poles of the same denomination in the two needles 

 being presented to each other, a repulsion took place, and the sus- 

 pended needle came to a state of rest between the opposing forces of 

 tonion and of magnetic repulsion. When the micrometer at E was 

 allowed to remain in its actual position, the suspended needle was 

 repelled 24 degrees, and consequently it was prevented from returning 

 to the rero point by a force of tonion expressed by the sum of 24 decrees 

 and of the horizontal force of terrestrial attraction ( = 24 x 35, or 810) ; 

 thus the whole force of magnetic repulsion was expressed by 864. In 

 a second experiment, the wire being twisted by making the stem at K 

 perform three revolutions (= 1080) in a direction contrary to that of 

 the 24 before mentioned, the needle rested at 17 from zero : the force 

 of magnetic repulsion was then expressed by the sum of 1097 degrees 

 and the value of terrestrial attraction ( = 17 x U5, or 595), that is, in 

 all, 1692 degrees. On comparing together several experiments of the 

 same nature, and also several similar experiments in which the poles of 

 a contrary denomination were presented to each other, Coloumb found, 

 neglecting small differences which may be supposed to have arisen 

 from the extent and configuration of the needles, that the forces of 

 magnetic repulsion and attraction vary inversely as the squares of the 

 distances. 



The "bifilar magnetometer" which was invented by M. Gauss, is a 

 species of torsion balance : it is described briefly in the article TERRES- 

 TRIAL MAGNETISM,, and at length in Taylor's ' Scientific Memoirs,' 

 vol. ii. The apparatus with which, by the oscillations of two balls of 

 lead at the extremities of a lever suspended horizontally by a string, 

 Mr. Cavendish determined the average density of the earth, was also a 

 Y^.ltwc acting on the same principle. [EARTH, MEAN DENSITY OF 

 THE.] The bifilar suspension has also been claimed, apparently with 

 justice, by Sir W. Snow Harris. See ' Rudimentary Magnetism," parts 

 i. and ii., p. 120, in which work, and also in the ' Rudimentary Elec- 

 tricity ' of the some author, the various torsion instruments used in 

 these branches of science are fully and satisfactorily described and 

 illustrated. 



For the strength of torsion hi machinery, see MATERIALS, STRENGTH OF. 



TORTOISE-SHELL. This beautiful substance, or at least the best 

 kind of the material which goes under the name, is procured from a 

 marine tortoise called the Hawk's-bill turtle, or Tcttuilo imbricata ; 

 the Latin name being derived from the mode in which the scales 

 upon the back are arranged, overlapping one another like the tiles upon 

 the roof of a house, one kind of which were called by the Romans 

 imlricet. In most other tortoises the several scales of which their 

 covering is composed adhere to one another by their edges, like inlaid 

 work. Each animal furnishes thirteen principal plates, five along the 

 centre of the back, and four on each side ; and twenty-five smaller 

 P^U. or plates, which constitute the margin of the nhi-11. The size 

 and thickness of the plates depend on the magnitude and age of the 

 animal, a fresh layer being produced every year ; and at the margin of 

 the Urge plates may be seen distinctly the edges of the layers as they 

 thin off in succession. The horny plates are separated from the bony 

 foundation by the application of heat ; the whole shell being commonly 

 placed over a fire until the plates begin to start from the bone, and the 

 separation being completed by the aid of a slender knife. The shell 

 varies much in value, being frequently injured by barnacles, limpets, 

 and other shell-fish adhering to the turtles while alive, and interfering 

 with the growth of the shell where they attach themselves. Occasion- 

 ally plates of a uniform yellow colour are met with ; and such are in 

 great request among the Spanish ladies, who will give at least twice as 

 much for a comb of plain tortoiseshell as for a mottled one. The 

 belly-plates of the tortoise are yellow, and are sometimes found suffi- 

 ciently clear for use. 



Before working, the shell needs to be softened or tempered, which is 

 usually done by dipping it for three or four minutes, or longer if it be 

 very thick and brittle, in boiling water. Some manufacturers flatten 

 and temper the shells with hot flat irons, similar to those used by 

 laundresses; the tortoise-shell being, in the course of the operation, 

 frequently dipped in cold water to prevent scorching. Generally, 

 however, the less the shell is heated and pulled about the better, 



because from its apparent want of grain or fibre it is apt to become 

 very brittle. Being also less fusible than horn, tortoise-shell cannot 

 be made soft enough to be moulded without some injury to the colour; 

 and accordingly the manufacturen, at least in England, never attempt 

 to produce tortoise-shell combs with ornamental open work by means 

 of dies. Such work is produced by pasting a piece of paper over the 

 tortoise-shell, drawing the pattern upon it, cutting it out with drills 

 and fine saws, and, after the paper has been removed by steeping in 

 cold water, finishing the ornaments with the graver. The cutting or 

 parting teeth of combs by machinery is described under COMB MAKV- 

 FACTUKK ; but we may here notice another mode which is occasionally 

 followed, and which illustrates the convenience arising from the flexi- 

 bility of the material when warmed. A piece of tortoise-shell, Urge 

 enough to make two combs, is bent or bowed in the direction of the 

 length of the teeth, to such a degree of convexity that they may be 

 cut with a straight bow-saw without cutting through either of the 

 edges of the pieces of shell, which are required to form the top or 

 back portions of the combs. The shell is then flattened and the ends 

 or points of the teeth are separated with a narrow chisel or pricker, 

 after which the combs are finished with files and scrapers, and bent to 

 any required curvature upon wooden moulds. The frames for tortoise- 

 shell eye-glasses are usually formed out of narrow slips of shell in 

 which slits are cut with a saw, the slits being subsequently, while the 

 shell is warm, ttraintd or pulled open, until they form circular or oval 

 apertures, by the insertion of tapering triblets of the required shape. 

 The same yielding or flexible property is made use of in the manufac- 

 ture of boxes; a round flat disc of shell being gradually forced by 

 means of moulds into the form ;of a circular box with upright sides. 

 The union of two or more pieces of shell may be effected by carefully 

 scraping the ports that ore to overlap, so as to render them jierfectly 

 free from grease, even such as might arise from being touched l>v tin' 

 hand, softening them in hot water, pressing them together with h t 

 flat tongs, and then plunging the joint into cold water. 



In veneering with tortoise-shell, by which very beautiful work may 

 be produced, it is usual to apply fish-glue, mixed with lamp-black, 

 vermilion, green, chrome, white, or other colouring matter, at the back 

 of the shell, both to heighten its effect and to conceal the glue or 

 cement by which it is secured to the wooden foundation. In making 

 knife handles and some other ornamental work, metallic foils are put 

 beneath the tortoise-shell veneer with excellent effect. 



The qualities of tortoise-shell as brought to market are thus dis- 

 tinguished : Manilla, fine and large ; Singapore, nearly as good as 

 Manilla; West India, large and heavy, but red; Honduras, darker, l>ut 

 with large dark rod spots ; Calcutta, dark, heavy, and badly coloured ; 

 Bombay, the worst quality. Sometimes plates are obtained as large as 

 13 inches by 8 inches, aud a quarter of an inch thick in the n 

 The price of the best tortoise-shell is generally about 60. per Ib. A 

 small import duty, formerly imposed, was repealed in 1846. 



TORTURE, which in a legal sense means the application of bodily 

 pain in order to force discoveries from witnesses, or confessions from 

 persons accused of crimes, has been recognised by the laws of most 

 civilised nations as an instrument for obtaining judicial truth. A 

 learned civilian terms it " Mos antiquissimus, omnium ferd bene insti- 

 tutorum populorum communis : ut uon iminerito pro lege ac jure 

 quodam gentium habeatur." (Wesenbechii, ' Paratitla ad Dig. de 

 Quscstionibus,' num. 3.) Torture was applied to slaves at Athens 

 (Demosthen., 'Orat. adv. Pantsenet.' ) ; and Cicero states that the 

 Athenian and Rhodian Uws allowed it to be applied even to i. 

 aud freemen (' Oratorio! Partit.,' 34) ; but there is some doubt as to the 

 accuracy of this statement with respect to Athenian freemen. It has 

 been questioned whether torture was used by the Itomans during the 

 republican period ; but Cicero frequently speaks of it as an ancient 

 practice, and attributes it to the customs and institutions of an earlier 

 age (" moribus majorurn "). (' Oratio pro Rege Deiotaro,' c. 1 ; ' Pro 

 Milone,' c. 22 ; ' Orat. Partit,' 34.) Tacitus also ascribes a modification 

 of the practice to an ancient Senatus-oonsultum (' Ann..' lib. ii., c. 30). 

 However this may have been, it is beyond all doubt that the use of 

 torture in judicial inquiries had become fully established in the t mu- 

 ff the early emperors. Regularly the Roman law admitted the torture 

 only in the case of slaves when examined either as witnesses or offend- 

 ers; but under the emperors even under Augustus, but more fre- 

 quently under Tiberius and Caligula instances occur in whi.-h freemen 

 and citizens were interrogated by torture : most of these instances, 

 r, are to be considered as irregular acts of power, not sanctioned 

 by Uw. Rules regulating the mode of applying torture, anil limiting 

 the occasions of its application, were early established in the Roman 

 Uw. One of the most important of these is that which Cicero in the 

 passages above cited refen to ancient usage, namely, that a slave should 

 not be tortured to give evidence against his master, except in the cases 

 of incest and conspiracy. Tacitus says that in order to evade the ope- 

 ration of what ho colls an ancient decree, prohibiting the " qusestio 

 ervi in caput domini," Tiberius, " novi juris rcpertor," invented the 

 scheme of making over the sUve from the accused to a public func- 

 tionary, and then putting him to the torture against his former master. 

 This device is however ascribed by other historians to Augustus. 

 (Dion., lib. Iv.) In judicial inquiries or public trials for crimes, the 

 " quicstio " was applied at the instance of the accuser in the presence 

 of the pnetor and judices, and the statements made under torture were 



