PHYSICAL OPTICS.- 137 



of colours in the lower parts of the rainbow, though they have 

 often been incomparably more vivid than the upper parts, 

 under wliich the colours have appeared. I have taken notice 

 of this fo very often, that I can hardly look upon it to be ac- 

 cidental ; and, if it fliould prove true in general, it will bring- 

 the difquifilion into a narrow compafs; for it will (liow that this . 



efl'ed depends upon fome property which the drops retain, 

 whiKi they are in the upper part of the air, but lofe as they 

 come lower, and are more mixed with one another." Phil. 

 Tranf. Vol. XXXII. p. 243. 



From a confideration of the nature of the fecondary rainbow, 

 of 54'', it may be inferred, that if any fuch fupernumerary 

 colours, were feen attending this rainbow% they would necelfa- 

 rily be external to it, inftead of internal. The circles fometimes . , 



(ieen encompaffing the obferver's (Imdow in a mift, are perhaps 

 more nearly related to the common colours of thin plates as 

 ieen by reileclion. 



IV. ARGUMENTATIVE INFERENCE RESPECTING THE 

 NATURE or LIGHT, 



The experiment of Grimaldi, on the crcfled fringes within Argumentative 

 (he (liarlow, together with feveral olhers of his obfervations/ 

 equally important, has been left unnoticed by Newton. Thofe 

 who are attached to the Newtonian theory of light, or to the 

 hypothefes of modern opticians, founded on views ilill lefs en- 

 larged, would do well to endeavour to imagine any thing like 

 an explanation of thefe experiments, derived from their own 

 do6lrines; and, if they fail in the attempt, to refrain at leaft 

 from idle declamation againft a fyftem which is founded on the 

 accuracy of its application to all thefe fads, and to a thoufand 

 others of a (imilar nature. 



From the experiments and calculations which have been Homogeneons 

 premifed, we may be allowed to infer, that homogeneous ^'g^^. I^^soppofitc 

 light, at certain equal diftances in the diredion of is motion, jiftances along its 

 is poflelfed of oppofite qualities, capable of neutralifing or coi'r^e, by which 

 deftroying each other, and of extinguifliing the light, where extinalon of" 

 they happen to be united ; that thefe qualities fucceed each the light may be 

 oiher alternately in fuccelfive concentric fuperticies, at dif- ^ ' 



tances which are conflant for the fame light, palling through 

 the fame medium. From the agreement of the meafures, 

 and from the fimilarityof the phenomena, we may conclude, 



that 



