TEL 



TEL 



the head, or terminate in an enlarge- 

 ment. 



TECTIBRANCHIA'TA {tectus, co- 

 vered, branchiae, gills). An order of 

 aquatic Gasteropods, which have their 

 branchiae situated on the back or on the 

 side, and' concealed or covered by the 

 mantle, as in the aplysia and the pleuro- 

 ^ branchus. 



TEGMEN. Literally, a covering; 

 hence, applied by Mirbel to the internal 

 integument of the seed, the endopleura 

 of Decandolle ; and, by Palisot de Beau- 

 vois, to the glume of grasses. 



TEGME'NTA (tegmentum, a covering). 

 In Botany, the scales of the bud. They 

 are termed foliaceous, when they consist 

 of abortive leaves ; petiolaceous, when 

 they are formed by the persistent base of 

 the petiole ; stipulaceous, when they arise 

 from the union of stipules, which roll 

 together and envelope the young shoot; 

 and fulcraceous, when they are formed 

 of petioles and stipules combined. 



TEI'NOSCOPE. Prism telescope. An 

 instrument formed by combining prisms 

 in a particular manner, so as to correct 

 the chromatic aberration of light, and to 

 increase or diminish the linear dimen- 

 sions of objects viewed through it. 



TELEGRAPH (r^Ae, afar off, Tpa^w, 

 to write). An apparatus for communi- 

 cating intelligence to a great distance, by 

 means of signals to which a conventional 

 meaning is attached. A telegraph is also 

 called a semaphore {ar\ixa, a sign, ^epo), 

 to bear); the latter term is, however, 

 more comprehensive than the former, as 

 it relates to the communication of intel- 

 ligence, not merely by signals resembling 

 written characters, but also by audible 

 signals, by beacons, and other pyrotechnic 

 contrivances. See Tellograph. 



TELEGRAPH, ELECTRICAL. An 

 apparatus for conveying thought by 

 means of the electric current, the sig- 

 nals being given by the different actions 

 of the current, which is carried from 

 station to station along insulated con- 

 ductors. The currents are excited either 

 by hydro-electric batteries, or by mag- 

 netic induction, and rotatory machines ; 

 the telegraphic signals are either the de- 

 flections of magnetized needles, or the 

 intermittent excitation of magnetism in 

 electro-magnets, or the physiological phe- 

 nomena. 



TELE'NGISCOPE (rrjXe, afar off, hf 

 71/?, near, aKoirew, to see). A new in- 

 strument, combining the powers of the 

 telescope and of the microscope. 

 330 



TELEOSAU'RUS (^eXeor, perfect, 

 aavpos, a lizard). An extinct genus of 

 Saurian reptiles, characterized by a com- 

 bination of a bi-concave structure of the 

 vertebree with long narrow jaws. This 

 genus, and that of the steneosaurua, have 

 been associated together by Professor 

 Owen, the characters of the two genera 

 being mainly derived from the difference 

 of position in the external nostril. 



TE'LESCOPE (T?jAe, afar off, aKoireu), 

 to see). An optical instrument for dis- 

 covering and viewing distant objects. 

 Astronomical telescopes are of two kinds, 

 refracting and reflecting ; in the former, 

 an image of the object viewed is formed 

 by a lens, termed the object-glass, which 

 refracts the rays from the object into one 

 point ; in the latter, the rays of light are 

 reflected by a concave speculum or mirror, 

 by which an image of the object viewed 

 is produced. The point where the image 

 is distinctly formed by the lens or mirror 

 is the focus ; and the distance of this 

 point from either the one or the other 

 is the focal length of the telescope. 



1. Reflecting telescopes are of three 

 kinds. 1. The Gregorian has a hole 

 pierced in the centre of the large mirror to 

 receive the eye-piece ; the rays from the 

 object falling on the large speculum are 

 reflected to its focus ; there they are 

 received by a small concave mirror, 

 whose focus coincides with that of the 

 large one, and reflected through the aper- 

 ture, where they are received, and the 

 image magnified by the eye-glass. 2. The 

 Cassegrainian telescope differs from the 

 above only by the small mirror being 

 made convex instead of concave. 3. The 

 Newtonian telescope has no aperture in 

 the large speculum, but the rays it re- 

 flects are received on a plane speculum 

 near the object glass of the tube, which 

 is fixed at an angle of 45° with the axis, 

 and by it are reflected to the side of the 

 tube, where the rays are brought to a 

 focus by the eye-glass. The telescope of 

 Lord Rosse is constructed on this prin- 

 ciple. 



2. Terrestrial telescope. The inver- 

 sion of the object is of little consequence 

 when the instrument is employed for 

 astronomical purposes, for since the forms 

 of the heavenly bodies are spherical, their 

 positions, in this respect, do not affect 

 their general appearance. But for ter- 

 restrial purposes, this is manifestly a 

 great defect, and therefore those con- 

 structed for such purposes as ship or spy 

 glasses, have two additional lenses, by 



