RAY 



RAY 



ble alteration. On the other hand, when expofed to the 

 other pencil, wiiich was much lefs briglit, and lefs hot, it 

 was blackened in lefs than fix minutes. M. Berard con- 

 cluded, from this experiment, that the chemical effedls pro- 

 duced by light arc not folely owing to the heat developed in 

 the body by its combining with the fubftance of the body^ 

 becaufe, on fuch a fuppofition, the faculty of producing 

 chemical combinations ought to be greatelt in thofe rays 

 which poffefs the faculty of heating in the greateft perfec- 

 tion : but perhaps we fhould lind Icfe oppofition between 

 thefe two opinions, if we attended to the different refults 

 which may be produced by the fame agent placed in dif- 

 ferent circumftances, and if we confidered that agents of a 

 nature quite diffimilar may determine the fame combinations 

 when they are employed. 



Various hypothefcs have been fuggefted in order to ac- 

 count for the properties above ftated. If wc wifli to con- 

 fider folar light as compofed of three dillinct fubttances, one 

 of which occafions light, another heat, and the third chemi- 

 cal combinations ; it will follow that each of thefe fub- 

 ftances is fcparable by the priim into an iiifinity of different 

 modifications, like light itfelf; fince we find, by experi- 

 ment, that each of the three properties, chemical, colorific, 

 and calorific, is fpread, though unequally, over a certain 

 extent of the fpeftrum. Hence we muft fuppofe, on that 

 hypothefis, that there exitt three fpeftrums one above an- 

 other ; namely, a calorific, a colorific, and a chemical fpsc- 

 trum. We mult, hkewife, admit that each of the fub- 

 ftances which compofe the three fpeftrums, and even each 

 molecule of unequal refrangibility which conititutes thefe 

 fubltances, is endowed, like the molecules of vifible light, 

 with the property of being polarized by reflection, and of 

 efcaping from rcfleftion in the fame pofitions as the luminous 

 molecules, &c. 



Inftead of this complication of ideas, let us conceive 

 fimply, according to the phenomena, that light is compofed 

 of a colleftion of rays unequally refrangible, and of courfe 

 unequally attrafted by bodies. This fuppofes original dif- 

 ferences in their fize and velocity, or in their affinities. 

 Why fnould thofe rays, which differ already in fo many 

 things, produce upon thermometers, or upon our organs, 

 the fame fenfations of heat or light ? Why (hould they have 

 the fame energy to form or feparate combinations ? Would 

 it not be quite natural that vifiou {hould not operate on our 

 eyes, except within certain limits of refrangibility ; and that 

 too little or too much refrangibility fhould render it equally 

 incapable of producing that effeft. Perhaps thefe rays may 

 be vifible to other eyes than ours, perhaps they are io to 

 certain ani-mals, which would account for certain aftions 

 that appear to us marvellous. In a word, we may conceive 

 the calorific and chemical faculty to vary through the whole 

 length of the fpcftrum, at the fame time with the refrangi- 

 bility, but according to different funftions ; fo that the ca- 

 lorific faculty is at its minimum at the violet end of the fpec- 

 trum, and at its maximum at the red end ; while, on the 

 other hand, the chemical faculty expreffed by another func- 

 tion is at its minim.um at the red end, and at its maximum at 

 the violet end, or a little beyond it. This fimple fuppofition, 

 which is only the fimple ftatement of the phenomena, equally 

 agrees with all the fafts hitherto obferved, and accounts for 

 thofe eftablifhcd by M. Berard, and even enables us to pre- 

 dift them. In fad, if all the rays, which produce thefe 

 three orders of phenomena, are rays of light, they mult of 

 courfe be polarized in pafiing through Iceland cryilal, or in 

 being refleftcd from a polifhed glals with a determined inci- 

 dence : and when they have received thefe modifications, 

 they muft be refloiSted by another glafs, if it is properly 



placed, to exert its reflefting energy on the luminous mole- 

 cules. On the other iiand, if that force is null on the vifible 

 luminous molecules, the invifible light will not be any longer 

 )-eflc£ted : for the caufe which occafions or prevents reflec- 

 tion appears to adt equally upon all the molecules, whatever 

 their refrangibility may be. It ought, therefore, to ad\ upon 

 the molecules of iuvifible light, the condition of vifibility 

 or in vifibility relating merely to our eyes, and not to the 

 nature of the molecules which produce thefe fenfations in us. 



This mode of viewing the facts appeared to Mefl'rs. Ber- 

 thoUet, Chaptal, and Biot, who made a report to the Inili- 

 tute on the Memoire of Berard, the molt natural and fimple ; 

 though the modeit referve of Berard reltrairied him from 

 deciding in a cafe, not fufBciently examined by the teft of 

 experiment. Annal. de Chimie, vol. Ixxxv. p. 309. or Thorn- 

 foil's Annals of Philofophy, N° 9. 



Ray, Common, in Optics, is lometimes ufed for a right 

 line drawn from the point of concourfe of the two optical 

 axes, through the middle of the right line which paflcs 

 through the middle of the centres of the pupils of the two 

 eyes. 



Rays, Cone of. See Cone. 



Rays, DefleSion of. See Deflectiom. 



Rays, Incimalion of incident. See Inclination. 



Rays, Optic. Set Optic. 



Rays, Rejlexibility of. See Reflexibility. 



Ray, Principal, in PerfpeSive, is the perpendicular dif- 

 tance between the eye and the vertical plane or table, as 

 fome call it. See Pekspective. 



Rays, Pencil of. See Pencil of Rays. 



Rays, Pyramid of. Sec Optic Pyramid. 



Ray of Curvature, in Geometry, is ufed to fignify the 

 femi-diamcter of the circle of curvature. See Radius and 

 Cukvature. 



Ray, Raia, in Ichthyology. See Raia. 



Ray, Cla-vated. See Raia Clavata, and Thornback. 



Ray, Eagle. See Raia Aquila. 



Ray, EleBric or Smooth, a fpccies of the raia. See Raia, 

 Torpedo, and Anatomy of Fish. 



Ray', Fuller, Raia fullonica, a fpecies of ray, deriving 

 its name from the inftrument which fullers ufe in fmoothing 

 cloth, the back being rough and fpiny. See Raia Fullo- 

 nica. 



Ray, Oblong. See Raia and Rhi.vobatos. 



Ray, Oculatek. See Raia and Miraletus. 



Ray, Rough. See Raia Rubus. At Scarborougli, 

 where it is common, it is called the white bans <■.- gullet. 



Ray', Shagreen, called at Scarborough the French ray, is 

 about the fize of the fl<ate, but narrower in Us form than 

 the common kinds. The upper part of the body is covered 

 clofely with fmall fhagreen-like tubercles, refembling the 

 Ikin of the dog-fifh ; and from the nole to the beginning of 

 the pedloral fins is a tuberculated fpace. Pennant. 



Ray, Sharp-nofed. See Raia Oxyrinchus. This fifh 

 makes a fnorting noife, and is fuppofed to be the bos cSf the 

 ancients, which Oppian defcribes as the broadefl among 

 fifhes, and fond of human flefh ; adding, that the method it 

 takes of deilroying men is by overlaying and keeping them 

 down by its vaft weight till they are drowned. Pennant. 



Ray, Sting. See Raia Pajlinaca, and Pastinaga Ma- 

 rina. 



RaY', in our Old Writers, a word appropriated to cloth 

 never coloured, or dyed, 1 1 Hen. IV. c. 6. Blount, 

 Cowel. 



Rays, in Botany, the fpreading marginal florets of a 



compound flower ; fee Radius. The fame term is applied 



to the fiib-diviiions of an umbel, more properly denominated 



I its 



