R I N 



in thin plates of various fubltances, by Mr. Boyle, and Dr. 

 Hooke, but afterwards more fully explained by fir Ifaac 

 Newton. Mr. Boyle having exhibited a variety of colours 

 in colourlefs liquors, by (haking them till they rofe in 

 bubbles, as well as in bubbles of foap and water, and alio 

 in turpentine, procured glafs blown fo thin as to exhibit 

 fimilar colours ; and he obferves, that a feather of a proper 

 fhape and fize, and alio a black ribband held at a proper 

 dillance between his eye and the fun, (hewed a variety of 

 little rainbows, as he calls them, with very vivid colours. 

 Boyle's Works by Shaw, vol. ii. p. 70. 



Dr. Hooke, about nine years after the publication of 

 Mr. Boyle's Treatife on Colours, exhibited the coloured 

 bubble of foap and water, and obferved, that though at 

 firlt it apppeared white and clear, yet as the film of water 

 became thinner, there appeared upon it all the colours of 

 the rainbow. He alio delcribed the beautiful colours that 

 appear in thin plates of Muleovy glafs ; which appeared, 

 through the microlcope, to be ranged in rings furrounding 

 the white fpecks or flaws in them, and with the fame order 

 of colours as thofe of the rainbow, and which were often 

 repeated ten times. He alio took two thin pieces of glafs, 

 ground plain and polilhed, and putting them one upon 

 another, prelled them till there began to appear a red co- 

 loured fpot in the middle ; and preflingthem clofer, he ob- 

 ferved feveral ring; of colours encompafiing the firft place, 

 till., at lalt, all the colours diiappeared out of the middle of 

 the circles, and the central fpot appeared white. The firlt 

 colour that appeared was red, then yellow, then green, 

 then blue, then purple, then red again ; yellow, green, 

 blue, and purple ; and again in the fame order, fo that he 

 fometimes counted nine or ten of thefe circles, the red im- 

 mediately next to the purple ; and the lalt colour that ap- 

 peared before the white was blue ; fo that it began with red, 

 and ended with purple. Thefe rings, he fays, would 

 change their places, by changing the polition of the eye, fo 

 that, the glades remaining the fame, that part which was 

 red in one pofition of the eye, was blue in a fecond, green 

 in the third, 5cc. Birch's Hi it. of the Royal Society, 

 vol. iii. p. 54. 



Sir Ifaac Newton, having deinonllrated that every dif- 

 ferent colour confilts of rays which have a different and fpc- 

 cific degree of refrangibility, and that natural bodies appear 

 of this or that colour, according to their difpolition to re- 

 flect this or that fpecies of rays (fee Colour), purfued 

 the hint fuggelted by the experiments of Dr. Hooke, al- 

 ready recited, and caiually noticed by himfelf, with regard 

 to thin it fubltances. Upon compreffing two 



prilms hard together, in order to make their fides touch one 

 another, lie obferved, that in the place of contact they were 

 perfectly tranfparent, which appeared like a dark fpot ; and 

 when it was looked through, it feemed like a hole in that 

 air, which was formed into a thin plate, by being impreffed 

 between the glafles. When this plate of air, by turning the 

 prifms about their common axis, became fo little inclined to 

 the incident rays, that fome ol them began to be tranfmitted, 

 there arofe in it many (lender arcs of colours, which in- 

 crealed, as the motion oi the pnlms was continued, and 

 bended more and more about the tranlparent fpot, till they 

 were completed into circles, or rings, furrounding it ; and 

 afterwards tin y bi Came continually more and more con- 

 tracted. 



By another experiment with two obje£t-glaflcs, he was 

 enabled to obferve diltinctly the order and quality of the 

 colours from the central fpot, to a very conliderable dif- 

 tance. Next to the pellucid central fpot, made by the con- 

 tact of the glafles, fucceeded blue, white, yellow, and red. 

 Vol.. XXX. 



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The next circuit immediately furrounding thefe confided of 

 violet, blue, green, yellow, and red. The third circle of 

 colours was purple, blue, green, yellow, and red. The 

 fourth circle confilted of green and red. All the fucceed- 

 ing colours became more and more imperfecl and dilute, 

 till, after three or four revolutions, they ended in perfect 

 whitenefs. 



In order to determine the thicknefs of the plate of air 

 by which he fuppofed the colours were produced, he mea- 

 fured the diameters of the firft fix circles, at their moft 

 lucid parts, and found their fquares to be in the arithmetical 

 progreflion of the odd numbers l, 3, 5, 7, 9, n • and hence 

 he concluded, that the intervals of ttie glaffes at thefe cir- 

 cles mult be in the fame progreflion. He alio meafured the 

 diameters of the dark or faint rings between the more lucid 

 colours, and found their fquares to be in the arithmetical 

 progreflion of the even numbers 2, 4, 6, 8, 10, 12 ; and he 

 concluded, after an accurate menfuration, the thicknefs of 

 the air at the darkeit part of the firft dark ring, made by 

 perpendicular rays, to be in the neareft round numbers 

 Tswirth part of an inch, half of which, multiplied by the 

 progreflion I, 3, 5, 7, 9, II, &c. gives the thicknefs of the 

 air at the molt luminous parts of all the brighteft rings, 

 their arithmetical means being its thicknefs at the darkeft 

 parts of all the dark ones. In examining the under fide of 

 the thin plate, in order to obferve what light was tranf- 

 mitted, he found that the central fpot was white, and the 

 order of the colours was yellowifh-red ; black, violet, blue, 

 white, yellow, red ; violet, blue, green, yellow, red, &c. ; 

 but thefe colours were very faint and dilute, except when 

 the light was tranfmitted very obliquely through the glafles. 

 When he put water between the glalles, and meafured the 

 rings again, he found the proportion of their diameters to 

 the diameters of the like circles made by air, to be about 

 7 to 8 ; fo that the intervals of the glafles, at fimilar cir- 

 cles, cauled by water and air, were about 3 to 4. 



When thefe rings were examined in a darkened room, by 

 the coloured light of a prifm call on a (heet of white paper, 

 they became more diftinct, and viiible to a far greater num- 

 ber than in the open air. He fometimes faw more than 

 twenty of them, whereas in the open air he could not dif- 

 cern above eight or nine. 



From other curious obfervations on thefe rings, made by 

 different kinds of light thrown upon them, he inferred, that 

 the thickneflcs of the air between the glaffes, where the 

 rings are fucceffively made, by the limits" of the feven co- 

 lours, red, orange, yellow, green, blue, indigo, and violet, 

 in order, are one to another as the cube roots of the fquares 

 of the eight lengths oi a chord, which found the notes in 

 an octave, fo!, la,fa,fol, /<;, mi,fa,fol; that is, as the cube 

 roots of the fquares of the numbers l, ;, ; , ; , ,■,.,, 

 Thefe rings appeared of that prifmatic colour with which 

 they were illuminated ; and by projecting the prifmatic co- 

 lours immediately upon the glafles, he found that the 1 . 

 winch tell on the dark places between the coloured rings. 

 was tranfmitted through the glalles without any change of 

 colour. From this circe. ' : that the origin 



oi thefe rings is manifeft ; becaufe tin- air between the glafles 

 is dilpoied, according to its \ariou... thicknefs, in fome places 

 to n lleCt, and in others to tranlir.it the light of any particu- 

 lar colour, and in the fame place to reflect that of one co- 

 lour, where it tranimits that of another. 



In exam , thi p lenomenaol 1. lours made by a denfer 



medium fusrounded b] a rarer, fuch as thofe which appeal 

 in plates ot Mulcovy glafs, bubbles of foaprand water, &c. 



the colours were found to be much more vivid than thl 



others, which were made with a rarer medium furrouml ■■ 1 



by 



