TEL 



Eff. C!i. Calyx of five leaves. Petals live-, inlerted into 

 the receptacle. Capfule with one cell, three valves, and many 

 feeds. 



1. T. Impetati. Green Orpine. Linn. Sp. PI. 388. 

 Willd. n. I. Ait. n. 1. (T. legitimum ; Cluf. Hill. v. 2. 

 67. Ger. Em. 520. Tilcpliio di Diofcor.ide ; Irapcrat. 

 Hift. Nat. 662.)— Leaves alternate.— Native of Switzer- 

 land, Italy, and the i'«uth of France. A hardy perennial, 

 kept in our botanic gardens, flowering in fumnier. Nu- 

 merous decumbent, round, herbaceous, leafy Jli-ms, a fpan 

 long, but flightly branched, fpring from the crown of the 

 root, fpreading in all dircftions. The leaves are fcattered, 

 nearly fcfiile, obovatc, entire, fmooth, ghiucous, rather fuc- 

 culent, an inch long, more or Icfs. Cymes terminal, foli- 

 tary, convex, of numerous {moolhjlo'wei-s, with white, or 

 pale flefli-coloured, petals. 



2. T. oppofitifoUum. Barhary Orpine. Linn. Sp. PI. 

 388. Willd. n. 2. (T. myofotidis foliis, amplioribus, con- 



jugatis ; Shaw Afric. n. 572. f. 572.) — Leaves oppofite.— 

 Found by Shaw in Barbary. Nothing is known of this 

 fpecies but from his rude figure, and (liort defcription. The 

 leaves arc elliptic-oblong, above an inch in length ; the lower 

 ones ftalkcd. Tops of the flowering brnnches recurved, as 

 in the Hellotropium. Petals fmall. Capfules of three valves, 

 with many feeds ; fo that there feems no doubt of the 

 genus. 



Telephium, in Gardening, furnilhes a plant of the fmall 

 hardy perennial kind, of which the fpecies ufually cultivated 

 for garden ufe is the true orpine (T. imperati). 



Method of Culture. — This plant is increafed by fowing the 

 feeds in the autumn or fpring, in dry light mould, either 

 where the plants are to remain, or in beds to be afterwards 

 planted out. They appear in the fpring, when they fliould 

 be kept clear from weeds, and they will flower the follow- 

 ing year. 



It is alfo capable of being increafed fometimes by offsets, 

 flips, or cuttings, planted out in the fpring feafon. 



It likes a dry light foil, in which it grows beft and lafts 

 longeft. The plants afford variety in the common borders 

 and clumps when placed in the fronts of thofe parts. 



Telephium, a mahgnant dangerous ulcer. The term 

 is derived from Telephus, who was wounded by Achilles, 

 and whofe wound, it is faid, became before he died a difeafe 

 of the above kind. 



TELEPHORUS, in Entomology, the Necydalis Ca- 

 rulefcens ; which fee. 



TELESCOPE, from T)l^:, at a d'ljlance, and o-xott/d, / 

 fee, is an optical inftrument that enlarges the vifual angle 

 fubtended by a diftant objeft, and thereby is faid to magnify 

 it, fo as to render it vifible to the eye of an obferver. This 

 property of niifking diftant objefts appear clofe to the eye, 

 never fails to excite the furprife of every one who looks 

 through a telefcope for the firft time ; but few, compara- 

 tively fpeaking, have their curiofity fully gratified, as' it re- 

 gards the means by which this wonderful phenomenon is 

 effefted. They are told, that the tube through which they 

 look, contains magnifying glaffes, or polilhed ijiecula, which, 

 by a pecuhar arrangement, produce the furprifing effeft they 

 witnefs, and there the explanation ufually ends ; but it is 

 our province to give our readers a better account of this 

 aftonilhing inftrument, which we propofe to do in a fyf- 

 tematic manner, firfl; by giving a fliort hijlory of its inven- 

 tion and improvements ; fecondly, by givmg a popular ex- 

 planation of the theory of the dioptric conftrudion, includ- 

 ing the doftrine of aberrations ; thirdly, by explaining the 

 theory of the cata-dioptric conftruftion ; fourthly, by de- 

 fcribing the jnoft approved infliniments, with reference to 



TEL 



the drawings that reprefent their figures on their refpeftive 

 Hands ; fifthly, by fliewing how their magnifying poiuers may 

 be meafured by dynametcrs, and varied by different arrange- 

 ments ; and lallly, by exemplifying their iifcs in meafur- 

 ing fmall angles and their correfponding terreftrial diftances. 

 But before we proceed further with this fubjeft, we muft 

 requeit our readers to perufe the articles Aberration, 

 Catoptrics, Dioptrics, Lens, Mirror, Reflection, 

 Refraction, and Speculum, in the preceding volumes 

 of our work, in order that we may not have occafion to 

 repeat what would otherwife have been neceffary to be in- 

 troduced in this place, to render our account fufficiently 

 full, particularly in that part of it which relates to the 

 theory of fingle lenfcs. 



I. The Hijlory. — The invention of the telefcope, which was 

 one of the nobleft that modern ages can boaft of, has ena- 

 bled man to raife his eyes far above the furf.ice of the globe 

 he inhabits, in fearch of worlds that v.-ere invifible to the 

 unaffiited eye ; and the more perfeft his inftrument is made, 

 the more celeftial bodies he difcovers fcattered through the 

 infinitude of endlefs fpace. Whether this invention, was 

 cafual, or the offspring of ratiocination, cannot perhaps be 

 pofitively affirmed from any exift^ing document ; but the pro- 

 bability is, that it was in a certain degree cafual : lenfes of 

 both the concave and convex formation were ufed feparately 

 to affift the human eye, antecedently to the conftruSion of 

 any telefcope ; and the general belief is, that fome accidental 

 placing of two lenfes, one convex and the other concave, of 

 different focal lengths, at fuch diftance from each other, 

 that the rays tranfmitted through them formed a pifture on 

 the retina of the eye, led to the difcovery that they poffeffed 

 the wonderful property of rendering a diftant body appa- 

 rently more large, and confequently more near, than it will 

 appear to the unaflifted eye, or to an eye ufing any fingle 

 lens whatever : this difcovery, once made, would obviouily 

 lead to the conftruftion ot an inftrument, in which this fimple 

 combination of two lenfes would be the bafis. 



The honour of having conftrufted the firft telefcope, 

 which was no doubt of the dioptric or refrafting fort, ( from 

 JioTTT^o", a perfpeciive injlrument,) has been attributed to va- 

 rious inventors, feveral of whom may have been equally en- 

 titled to the claim of originality, though only one can be 

 confidered as the Jirjl inventor. We profefs not to be in 

 poffeflion of better information on this fubjeft than our pre- 

 deceffors were, and therefore fliall fatisfy ourfelves with the 

 enumeration of thofe perfons who appear to us worthy of 

 being put on the lift of competitors for the honour of this 

 noble invention. Mr. W. Molyneux has alferted, in his 

 " Dioptrica Nova," that our countryman Friar Bacon well 

 anderftood the nature of all forts of optical glaffes, and 

 how to combine them fo as to form fome fuch inftrument as 

 the telefcope ; and Samuel Molyneux, the Ion, has affirmed, 

 that not only the invention but conftruftion of a telefcope is 

 fairly attributable to Bacon, as may be collefted from various 

 Latin phrafes in his Opus Majus; and Dr. Jebb, who edited 

 this work, adduces a paffage from Bacon's maiuifcript, to 

 prove that he aftually applied telefcopes to aftronomical 

 purpofes fo long ago as in the 13th century ; the friar hav- 

 ing died in the year 1294. 



The paffages to which Mr. Molyneux refers, in fupport 

 of Bacon's claims, occur in his Opus Majus, p. 348, and 

 P- 357- Jebb's ed. 1733. The firft is as follows: " Si 

 vero non fint corpora plana, per quje vifus videt, fed fphae- 

 rica, tunc eft magna daverfitas : nam vel concavitas corporis 

 eft verfus oculum vel convexitas :" whence it is inferred, 

 that he knew what a concave and convex glafs was. The 

 fecond is comprifed in a whole chapter, where he fays, " De 



rlfion? 



