CHR 



CHR 



With respect to transparent coloured bo- 

 dies, he thus expresses himself: ""A 

 transparent body, which looks of any co- 

 lour by transmitted light, may also look 

 of the same colour by reflected light ; 

 the light of that colour being reflected by 

 the farther surface of that body, or by 

 the air beyond it: and then the reflected 

 colour will be diminished, and perhaps 

 cease, by making the body very thick, 

 and pitching it on the back side to dimi- 

 nish the reflection of its farther surface, 

 so that the light reflected from the ting- 

 ing particles may predominate. In such 

 cases the colour of the reflected light 

 will be apt to vary from that of the light 

 transmitted." 



To search out the truth of these opi- 

 nions, Mr. Delaval entered upon a course 

 of experiments with transparent colour- 

 ed liquoi's and glasses, as well as with 

 opaque and semitransparent bodies. And 

 frpm these experiments he discovered 

 several remarkable properties of the co- 

 louring matter ; particularly, that in trans- 

 parent coloured substances it does not re- 

 flect any light ; and when, by intercept- 

 ing the light which was transmitted, it is 

 hindered from passing through such sub- 

 tances, they do not vary from their form- 

 er colour to any other, but become en- 

 tirely black. 



This incapacity of the colouring par- 

 ticles of transparent bodies to reflect 

 light, being deduced from very numerous 

 experiments, may therefore be taken as 

 A general law. It will appear the more 

 extensive, if it be considered that, for the 

 most part, the tinging particles of liquors 

 or other transparent substances, are ex- 

 tracted from opaque bodies; that the 

 opaque bodies owe their colours to those 

 particles in like manner as the trans- 

 parent substances do ; and that by the 

 Joss of them they are deprived of their 

 colours. 



Notwithstanding these and many other 

 experiments, the theory of colour seems 

 not yet determined with certainty. The 

 discoveries of Sir Isaac Newton, how- 

 ever, are sufficient to justify the following 

 aphorisms. 



1. All the colours in nature arise from 

 the rays of light. 2. There are seven 

 primary colours ; namely, red, orange, 

 yellow, green, blue, indigo, and violet. 

 3. Every ray of light may be separated 

 into these seven primary colours. 4. The 

 rays of light, in passing through the same 

 medium, have different degrees of re- 

 frangibility. 5. The difference in the co- 

 . lours of light arises from its different re- 

 frnngibility : that which is the least re- 



trangible producing red ; and that which 

 is the most refrangible violet. 6. By com- 

 pounding any two of the primary, as red 

 and yellow, or yellow and blue, the inter- 

 mediate colour, orange or green, may be 

 produced. 7. The colours of bodies 

 arise from their dispositions to reflect one 

 sort of rays, and to absorb the others ; 

 those that reflect the least refrangible 

 rays appearing- red, and those that reflect 

 the most refrangible violet. 8. Such bo- 

 dies as reflect two or more sorts of rays 

 appear of various colours. 9. The white- 

 ness of bodies arises from their disposi- 

 tion to reflect all the rays of light pro- 

 miscuously. 10. The blackness of bo- 

 dies proceeds from their incapacity to 

 reflect any of the rays of light. And 

 from their thus absorbing all the rays 

 of light that are thrown upon them, it 

 arises, that black bodies, when exposed 

 to the sun, become hot sooner than all 

 others. 



Sir Isaac Newton, in the course of his 

 investigations of the properties of light, 

 discovered that the lengths of the spaces 

 occupied in the spectrum by the seven 

 primary colours exactly correspond to 

 the lengths of chords that sound the se- 

 ven notes in the diatonic scale of music ; 

 which is made evident by an experiment. 

 On a paper, or other fit substance, in a 

 darkened room, let a ray of light be re- 

 fracted by means of a prism into a spec- 

 trum of some size, marking upon it the 

 precise boundaries of the several colours, 

 and it will be found that the spaces by 

 which the several colours are bounded, 

 viz. the space containing the red, that 

 containing the orange, yellow, &c. will 

 be in exact proportion to the divisions 

 of a musical chord for the notes of an oc- 

 tave ; that is, as the intervals of these ; 1 

 8.5.3.2.3. 9.1 See Co- 

 7 i V > * > ~S > T J r ) 2' 

 Lotrns, OPTICS, &c. 



CHROME, a metal discovered by Vau- 

 quelin. It exists in the state of an acid, 

 combined with oxide of lead, in a beauti- 

 ful mineral named red lead, found in Si- 

 beria, and with regard to which very dis- 

 cordant analyses had been given by dif- 

 ferent chemists. Vauquelin reduced the 

 metallic acid which he discovered in it to 

 the metallic acid, and his researches have 

 been confirmed by those of Klaproth and 

 Gmelin. It derives its name from the 

 splendid and numerous colours which it 

 presents in its saline combinations. It 

 lias since been discovered in various mi- 

 7ierals. The native chromate of lead, or 

 the red lead of Siberia, is generally crys- 

 tallized in oblique tetrahedral prisms. Its 

 colour is a fine aurora red ; its lustre 



