V 



and the reft, as each exceeds another in mapnlti^ \> 

 fo it is turned out of its right line with n.uch .,iffi' 

 culty, and lefs confiderably. 

 Now each ray of light, as it differs from another )n 



its degree of refrangibility^ 

 it in colour. 



fo likewifc it dillcrb from 



ments. 



14. Tht^y own that as the coloured body is not imme- 

 diately applied to the organ to occalion r!'.e fcnlation, 

 as no body can affec5t the ienfe but by imnicdiate con- 

 ta(5t, the coloured body does Hot extiie the fenfation 

 of itfelf, or contribute any t:hing to it, otherwife than 



■ by moving fome interpofed itiedium, and by that the 

 organ of fight. 



15- They add, that as it is fouhd that bodies do not 

 afFe<5t the fenfe in the dark, and that light only occa- 

 fions the fenfation of colour, by moving the organ ; 

 and that coloured bodies are no farther tohcbrncd than 



in rcflecSting the light in a certain modification j the ..., , ^., „,^ vi^^i.^^ piupa-atca ir 



difference in colours, according to them; arifeS in a fibres of the optic nerve into the bram, then 

 difference in the texture of their parts, by which they > - - ■ -,^. - 



are difpofed to refleft their light with this or that mo- 

 dification. ' V 



This is warranted by nun^crous expcri- 



l^hofc particles which are more refracted, are found 

 to cdnftitute a ray of a Violet colour -, i. e. in ailpro- 

 biibihty, the moft minute particles of light, thuj fc- 

 parately impelled, excite the Ihorteft vibration 



the retina, which are thence propagated 



the foJid 



i i 



c to excite 



t6. Dr. Hook, in his Micographia fays, The phan- 

 tafm of colours is caufed by the fenfation of the ob- 

 lique or uneven pulfe of light, and that this is capa- 

 ble of no more varieties than two, which arife from 

 the two fides of the oblique pulfe -, fo that there are 

 in reality but two fimple colours, yellow and blue ; 

 from the mixture of which, and a due proportion of 

 black and white (that is, darkr.efs and light) all colours 

 may be be produced. 



17. But this pha^nomenon of nature and colour, hav- 

 ing long perplexed philofophers to account forthedif- 

 coveries relating thereto, the incomparable Sir Ifaac 

 Newton found by two experiments on prifms, that 

 there is a great deformity in the rays of light, and 

 , that hereby the origin of colours may be unfplcled. 

 The dodrine of colours therefore, according to his 

 notion and experiments, are contained in the foUow- 

 ing propofitions : 



I. That light confifts of an infinite number of rays, 

 right lined and parallel, but of different ciegrees of 

 refrangibility, when meeting with' a different me- 

 dium. \ ... .;.,>,' ' 

 \ Each ray, according to^ i^s, degree of refrangibiljty, 



^^^J^ (o refraded^ appe^s to. the,?ye. of ^ diifcrent 

 colour. , -; . ^"i _' . . 



the fenfation of Violet Colour, as being the moil dulky 



and languid of all colours. 

 Again ; 



thofe particles which are the moft refracled 

 conftitute a radiolus, or little ray, of a red colour • 

 ' i. c. the largeft pardcles of light excite the longeft vi- 

 brations in the retina, fo.as fi excite the fenfauon of 

 fed colour, the brighteft and moft vivid of all colours. 

 It is remarkable, that in.the growing of plants, the 

 fame plants do from time to -time, alter and chano-e 

 their colours as the veffels which are in their youno- 

 Ihoots grow l^iger. ^ The leaves are of a faint yellow 

 when theyarfejn their fmallerftate, but they become 

 of a bright green,^ or fometimes red, when they are in 

 their middle ft^te f but when their veffels are enlarged 

 to their full growth,- they become of a dark green, and 

 then change to a fetiillemort colour towards autumn, 

 from the ripening of their juices ; from thence to pu- 

 trefadion, which refolves itfelf again into earth, its 

 firft principle. 



VASCULIFEROUS PLANTS are fuch whofc 



feeds are contained in veffels, which are fometimes d:- 



either uniform or difform. 



ASES: A Vafe is ,1 fort 



garden. 



'nopetalo 



fiower 



1 ■' - 



— '- - ^ 



3. 1 ne lealt trangible rays appea^ of a 4eep fcarle 

 qolour i the moft refra,ngible appear pf a, Violet blue 

 *J? Inteirmediate proceeding from fcarlet; to yellowiih 

 then to light green, and fo to bfue."* ' ~ 



.4- The colours .afifjng from the different degreeTof 

 refrangibihty of light a;-e not only the more noted* co- 

 lours of red, yellow, green and blue, bur aifo all the 

 intermediate colours of red to yellow, of yellow to 

 green, &c. 



5. Whitenefs, (fuch as the fun's light appears,) con- 

 taining all thofe degrees of refrangibility, is confe- 

 quently niade up of all the above-mentioned colours. 



6. Simple or hpmogeneal colours, are {yiqk as are 

 produced by Ijomo^eneal lights' or rays, which have 

 ^h^fame dfigret; of refrangibility ; and mixed colours 

 are fuch as are produced by rays of different refranc^i- 

 bility.. . _. . ■ ■. •., _. ■ • :, ■ ° 



j. Rays of the fame refrangibility produce the fame 

 colour ; ^yhich colpur is not alterable by repeated re- 

 fradlions, but only made ftrongor faint, as the rays 

 are united or fcattered. ...-.,,. 



. I 



i 



J T 



>, J ^ 



■ ' - 



I V 



35 their furfaces are adapted to refleft only the ravs 



ot luch a colour : or at leaft in more plenty than the 

 reft. , ... J 



But to explain thefe things farther : : . 

 It is fouhd by experience, that rays or beam.s of light 

 are compofed of particles very heterogeneous or dif- 

 fimilar to each other! i.e. fome of them, as it is 



; %hly probable, are larger, and others lefs ; for a ray 

 of hght, being received on a refrafting furface in a 

 dark place, is not wholly refrafted, but fplit as it were, 



. and diffufed mto leveral little ravs ; fome of which 

 ?'"^Jf=fr2'<?ed to the extreme points, and others to the 

 intermediate pomts -, i. e. thofe particles of the light, 

 which are moi;t minute, are diverted the moft eafily 

 ^^ '^^^^^^"fi'icrably of all others, by the adion of 

 the refrafting furface, out of their redlilinqal courfe ; 



VEGETABLE, a term applied to all plants, con- 

 fidered as capable of growth ; i. e. to all natural bo- 

 dies, which have parts organically formed for gene- 

 ration and accretion, but not for fenfation.' 



Dr. Boerhaave defines a Y<„ , _ 



; vrated of the earth, to which it adheres, and Is con- 



i , ne<5bed by parts called roots, through which it receives 



f i. the matter of its nouriftiment and increafe, and con- 



fifts of juices and veffels, fenfibly diftinft from each 



other ; or a Vegetable is an organical body, compofed 



of veffels and juices every where diftinguifhable from 



each other, to which the roots grow, or parts by which 



it adheres to fome other body, from which it derives 



~ the matter of its life and growth. 



This definition of a Vegetable is very fcientific, and 

 furnifhes us with a juft and adequate idea of it -, for 

 by its confifting of veffels and juices, it is diftinguiflied 

 from afoffil; and by its adhering to another body, 

 and deriving its nourifhment therefrom, it is diftin- 

 guiihed from an animal. . - — 



He defines a Vegetable an organical body, becaufe it 

 confifts of different parts, which jointly concur to the 

 exercife of the fame funftion. . 

 The definition of its adhering by fome of its parts to 

 another body is very proper ; for we know of no plant 

 , that is fo abfolutcly vague and fluftuating, but has 

 ftill a body it adheres to, though that body may be 

 various, e. g. earth, as in our common plants ; ftone, 

 as in rock plants ; water, as in fea plants; air, as in 

 fome mucilages. 



As to thofe few plants that appear to float with the 

 water^ their manner of growth is fomewhat anoma- 

 lous. Monfieur Tournefort has ftiewn. That all plants 

 do not arife ftridly from feeds ; but that fome, inftead 

 offemen, depofit or let fall a drop of juice, which 

 finking in the water by its gravity, reaches the bottom, 

 or fqme rock, &c. in its way, to which it fticks, 

 ftrikes root, and fhoots into branches: fuch is the 

 origin of coral. ' 



To which may be added. That a root of a plant may 

 have any fituation at pjeafure, with refped- tothe 



body 





