R I N 



equally well obtained by the ufe of a prifm, but he has alfo 

 (hewn, that the great fimplicity of this valuable optical 

 inftrument has cleared up great difficulties, by pointing out 

 to us that the colours which are modified into fuch various 

 fhapes, are in all prifmatic experiments exclufively produced 

 by the critical feparation of the rays of light. As this fa£t 

 mud be admitted, it certainly will not be philofophical to look 

 for a different caufe of the fame or iimilar effefts, when convex 

 glaffes, which have all the required prifmatic properties, are 

 tifed to produce them. In order to (hew the great fimila- 

 rity, or rather the identity of thefe effects, it will be fufficient 

 to take the molt fimple cafe of each, namely, the coloured 

 rings that are produced when a plano-convex lens is laid with 

 its convex fide upon a plain reflecting furface : and the co- 

 loured ftreaks which are produced when the bafe of a right- 

 angled prifm is in the fame manner placed upon fuch a furface. 

 The refults of the experiments, with the reafonings annexed 

 to them, are contained in the following propositions. The 

 form of rings arifes from the fpherical figure of the lens : the 

 right-lined appearance of the ftreaks is owing to the ftraight 

 figure of the plain furface of the prifm. The colour of the 

 rings may fuddenly be changed ; the colours of the blue 

 bow-ftreak may as inftantly be converted into thofe of the 

 red bow. The caufe of the fudden change of the rings has 

 been (hewn to be that the fets of one colour are feen by reflec- 

 tion, and thofe of the other by tranfmiffion ; it lias alfo been 

 fhewn, that the blue bow-ftreaks are feen by reflection, and 

 thofe of the red bow by tranfmiffion. In a lens we may, at 

 the fame time, fee, in half the fet, the colours of the reflected, 

 and in the other half, the colours of the tranfmitted rings ; 

 and in a prifm held before an open window, when the eye is 

 clofe to it, and when half the bow falls on the fide of the 

 room, we may fee blue ftreaks by reflection from half the 

 blue bow, and green ftreaks by tranfmiffion from half the 

 red bow. When deep convex, or concave, glades are laid 

 upon the lirlt furface of a lens, the rings are not affeCted by it ; 

 and when the fame glaffes are laid upon the fir ft furface of a 

 prifm the ftreaks remain unaltered. When the convexity of 

 the less, which is placed on the reflecting furface, is changed, 

 the fize of the rings is alfo changed ; and when the angle of 

 the prifm is increafcd or diminiflied, the diltance of the ftreaks 

 undergoes a proportional alteration. When the lens is 

 preffed upon the plain glafs, the rings increafe in diameter ; 

 and by a preffure of the plain glafs againft the prifm the 

 diftance of the ftreaks grows larger. To form rings by a 

 lens, fcattered rays only are required : and the fame light is 

 belt for the production of ftreaks by a prifm. Many other 

 inftances of similarity might be adduced, but it is needlefs. 

 Now, as it has been clearly proved, that the critical fepara- 

 tion of the colours, which takes place at certain angles of 

 incidence, occafions all the phenomena of the blue and red 

 bows, and of the ftreaks, rings, and other regular or ir- 

 regular appearances, that may be feen in a prifm, it cannot 

 be doubted that the Newtonian rings obferved between 

 objeCt -glades are owing to the fame caufe. 



Dr. Herfchel concludes an elaborate paper on this fubjcCt 

 with the following remarks on the Newtonian alternate fits 

 of eafy reflection and eafy tranfmiffion. 



" In attempting to refcue the feienceof optics from what 

 has been fo long confidred as unfatisfaCtory for explaining 

 the great queftion about the caufe of the coloured rings, 

 I have made ufe of a principle, the effeCts of which have fo 

 near a rcfcmblance to thofe of the fuppolititious fits of eafy 

 reflection and eafy tranfmiffion, that the author of them might 

 eafily be midcd by appearances. But although the principle 

 of a critical feparation of the colours, fubltitutcd tor thefe 

 fits, admits the reflection of fome rays at the fume angles of 



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incidence at which others are tranfmitted, yet fince the 

 Newtonian different rcfrangibility of light will account 

 for thefe critical reflections within glafs, and equally critical 

 intromilfions from without, we can have no longer any reafon 

 to afcribe original fits to the rays of light, which in the firft 

 part of this paper they have already been proved not to pof- 

 fefs, and which now, in all prifmatic experiments, I have 

 fhewn are not neceffary for explaining appearances that may 

 be accounted for without them." 



In the Philof. TranfaCtions for 1S10, vol. c. pt. 2, we 

 have a third paper, as a fupplement to the other two papers, 

 containing additional obfervations on the caufe of coloured 

 concentric rings between objeCt -glaffes, and other appearances 

 of a iimilar nature, in which Dr. Herfchel further explains 

 what fome may have thought obfeure, and obviates certain 

 objections againft his theory. His fundamental principle 

 for explaining the colour of the rings, which he has illuftrated 

 both by reafoning and experiment, is this : that the colours 

 in all prifmatic phenomena are produced either by the inte- 

 rior critical feparation arifing from the different reflexibility 

 of the rays which caufe the bine bow, or by the exterior 

 critical feparation arifing from the different intromiffibility 

 of the rays which caufe the red bow. In this paper he fub- 

 joins fome additional arguments to thofe before given, in 

 order to prove, that there are two primary prifmatic bows, 

 a blue one and a red one; and he maintains, that the red 

 bow is a phenomenon of equal originality with the Newtonian 

 blue bow, and that as one of thefe bows cannot be the con- 

 verfe of the other, we have two critical feparations effentially 

 different, viz. the reflective and intromiffive. But we muft 

 refer to the author's own account, uhi fupra. 



For an account of the rings of colours produced by elec- 

 trical explofions, fee Colours of Natural Bodies, Circular 

 Spots, and Fairy Circles. 



Rings of Flies, in Natural Hi/lory, the feveral rounds or 

 circular portions, of which the bodies of thefe and other 

 infeCts are compofed. 



In the fly kind thefe are cruftaceous or cartilaginous, and 

 confequently of a matter little capable of extenfion ; many 

 aCiions of thefe infeCts require, however, that their bodies, 

 or a part at leaft of their bodies, (houldbe able to inflate or 

 diftend, and contract their fize occafionally. Were every 

 ring of the body one entire fcale, or ihelly fubftance, thefe 

 changes could not be eafily effected ; nature has therefore 

 fo provided, that the tender bodies of thefe little creatures 

 are fufficiently defended, and yet all the neceffary motions 

 may be performed. 



Ring, in Agriculture, a fort of hoop made of iron, 

 which is ufed tor various purpofes, as fattening horfes and 

 cattle by in the flails. In thefe cafes they fliould be made 

 large and ftrong. 



Ring, in Commerce, a term ufed in reckoning at Ham- 

 burgh, and is equivalent to 240 of things that are fold by 

 number. Staves are fold in rings of 4 fchoaks (a fchoak 

 being 60) and 8 pieces : 3 rings of bogfhead ftaves, or 6 

 rings of barrel ftaves, are reckoned equal to 2 rings of pipe 

 ftaves. 



Ring, a (lout circle of iron in the upper part of the (hank 

 of an anchor, to which the cable is bent. 



Rings are alfo circles of iron or other metal, let over the 

 points of bolts, whereon they are clenched, to prevent their 

 drawing. Hatch-ring 1 ;, or ring and (tarts, are thofe which 

 are fixed in the hatches or [cuttles to open or (hut them 

 with. 



RlKGS in Timber, in Rural Economy, the concentric layers 

 by which the wood is formed. Thefe rings are, according 

 to Dr. Darwin, annually produced from the alburnum, and 



arc 



