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SPECIMEN DEFINITIONS FROM THE CENTURY DICTIONARY 



Issued by the ^fje ®|11C^ 



ray 



Exlr.iurthnary ray. Sit- r./n/< //-'/(. Hcischclian rays 

 uf the speclrum- Sec J/ttsiMuin. Medullary rays. 

 I.I I St-i- nutiuliiiiy. f/) HujkUcs i»f slniinlil ^'r lollivtin^; lubtik-N 

 ot thi! kiiliu\ (.vuiUiiiii*.! in lliir cortex ; tlie pynimivU ol bVrrcin. 

 See /■/(/■/(/.. Ubscure rays. St-i* o/'siun- and sf-t'ctrum,— 

 Ordinary ray. S.c feft-m //<»«.— Principal ray. Sec 

 /v*/«, '/.(/. Ritleric rays. Sec A'/V/.Wc. Visual rays. Sec 

 I'iAMdA Cathode rays, a form ol' radiation jfcni-ralcJ in a 

 vaciiuni-tuhc. in connLVtion with the catlutiic. or nc-nalivc pole, 

 wlirn .'in ekvtric ilJM'harye is passcil throujjh it. X-rays^ or 

 Rontgen rays, a form ol radiation liaxin^ cliarat,terlstic .inJ 

 (lisliiu'live properties. tiiM-'ox cred hv rr^ilessor Wilhehn Ki>iirad 

 U'>nlK»'n. **' W'lir/biirjj (aniu^mu'ed by hiin in nefeiiiluT, iS<)5K 

 ile slii»\veil that the di^L■har^;e ot ;( lar^Je Kidnnkorrt coil throu^;lI 

 a \aciiuni-tube jtro^hices ;i form ot" radi.'ition external lo the 

 laltcr. «hich b.is t'-e pr^ipert) »<!' causinj^' various suhslaiices to 

 Ihioresce : v>f' atVictin;^ the ordiii.ir) phiU»»j,'r.iphic plate like li^ht 

 (ihtui^h itself invisible); ami ot" penetrating: op.tqiie bo^Ues in 

 \ariinis tlenree>, accortlin^; ti> lliclr ilensilj and rel.ilive tliickness, 

 platinum, Ictil, .and silver bein(^ ipiite op.uiiie. while aluminium. 

 wood, and paper are ijuite lransp;irenl. lie also found tliat these 

 rays arc not refracted by prisms \yi carbun disidphid, and th;it 

 uncertain refractivui v>ccurs with \iilc.'inized rubber prisms ;»nd 

 those made oi alumintimi ; that powdered substances, o|iai|uc to 

 white li^ht, arc miile as transparent to these rays as solid Ixulies 

 vtf equal mass; .-ind that bi'dics h;i\'in^ roueh surfaces :ict like 

 those ^vhv>se surfaces ;irc polished. 'I'hese facts forced him tt> 

 conclude that retraction and ^c^'ul.■lr rcllection do not exist, but 

 that such lH>dics beha\c ti< X-^a^■s ;is muddy medi.a l^i lit^ht. 

 Other conclusions were th.at these rays pass throuf,'h ;»1I 

 s\ibslances at the same speed : ih.it air absorbs a \ery nuich 

 smaller part \>i ihem than \>i catbotle r.iys ; that tlie\ are not 

 dellected b\ a magnet ; that the spot on the wall ol the tube 

 which Huoresces most decidedK is tv> be rcR-irdcd as the principal 

 |ioint o^ their radiation ; that when the cathode rays are dcHected 

 within the tube, the spvit is ch.-in>;ed, thus pri,>ducin^j a new source 

 ot radiation ; that, tnereforc, cathode rays and X-r.iys arc not 

 identical ; that X-rays arc rcctilincarly propa^^atctl ; that no 

 interfereiice pbeniimena of X-rays were found to exist ; th,-it the 

 ;ibi>ve facts tend to shou that they have properties not hitherto 

 known in connection with ultra-\iolet. visible, and infra-red 

 lijjiit ; and that, therefore, they do not consist of transverse 

 vibrations s>i the ether, but K^i longitudinal vibrations. Tlie 

 source ot X-rays has been shown to be the surface upon which 

 the cathode rays first strike, whether that surface be the wall of 

 the tube or an object placed within the tube: when this object 

 within the tube is the aninle itself, the emanations are most 

 powerful. It has also been Uiund that X-rajs ha^e the properly, 

 in common with ultr.a-violct lijjht. of dispersing nej?.ative charges 

 on insulated surfaces and the pi^wer ot pv->sitivel\ electrifying- 

 svicb svirfaces ; and that rej^ular retlectit>n, tboujjh weak, ma>- be 

 demonstrated by the use of tile pliotofjrapbicj plate ;tnd lon^; 



in. 1 1. . i / li.i.i I'leviousty hhown that c^iihoUc ray* 

 peiiL-irate o|>.u|ue lH>dies, and Lenard that stieh ravit may pantt 

 throuKl) aluminium forming a part i.-'i the wall of tlie tube and 

 alTect the photo^r.'ipbic plate, but that llieir absorption ih 

 excessi\e beyond a few miUtmctcrH from the aluminium window, 



Diatomacese (cH"a-l*'»-masc-c), n, pL INF-, < 

 Dialoma -|- ■iu\-u.\ An order of niicn^scnpic tinictlitilar- 

 alj^iu, much rcsuiuldin}^ ihc * Dcsf/iidiiui,!., from which 

 they arc dislinj^uishcd hy 



a silicification of the ccl 

 wall and I>y the presence 

 of a ijrownish pigment 

 which conceals ihe yreen 

 of the chloropliyl. The 

 Cells are either isolated or 

 united into threads, etc., and 

 olten secrete a thin jeily in 

 in which they live socially. 

 liach fruslule is ct>mposed 

 oi two separate and smiilar 

 parts (vaKes), the cdg"es ot 

 which usually fit one oxer 

 the other like the lid of a box. 

 Reproductii>n takes pl.'icc 

 as in the desmids, in two 

 w.ays, by division and by sex- 

 u:ilconjuj;;ition. Diatoms ex- 

 ist in all parts ot the world 

 in immense numbers at thf 

 bottom of the sea and oi 

 tVesh water, and arc .also 

 fourd attached to the sub- 

 merjfcd parts of aquatic 

 plants, etc., and amon^ 

 mosses and in other d.amp 

 localities. There are many 

 R-encra, and the number of 

 known species exceeds 1,500. 

 They vary g^reatly in the form 

 and marking oi the valves. 

 which arc often exquisitely 

 sculptured, forming beauti- 



/1\ 



11/ 







-111 



A 



a 



Diatoinamr, iiMijiiilicd. 



(I, >'uuii>; nidiviiiiMlsur Ct^icn'iHa ian- 

 i^o/titiiHi; A. loiiji:iliitl)ii»1 view of ;t sin^lf 

 fnistulc o( Strialflia inttrruf'la, nIiow- 

 in^: strife ; c, ilomfiuuttnut hyalimiiit, 

 ntt.icliC(t 10 .1 rilaMRMit uf Lon/rn-a : rf. 

 Sfriatflta inferru/>ta : ni.uiy imlividti.ilN 

 united lilcT.dty lo fonii .1 'str.iii->li.i|H.*d 

 cttluriy with ;i Literal |>c<li(X'l. (("'roiii I.c 

 M.ioiit .iii<l Deciisric's "Traitc yciicral 

 di: Hot.ini.iiir."> 



ful i>bjecls under the Inicroscope and testinc its hif^hest powers. 

 In some species the lines arc found to equal 1^5, uoo to tne inch. 

 Extensive fossil depv'isits of the sjlicious rem.iins of /yiatoniact'tr 

 oe'cur in various kx-:ilitics. as at Rilin in Mohcmia, and in V'ir- 

 j^inia, Nevada, and California. They are sometimes used as 

 polishinjj-powder. The\ ;ire .abundant in j^tiano. .\tso called 

 fimillttriaciir. 



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