MifceUanea Curio fa. 37 



in theft Defcriptions, the Rainbow it felf be- 

 ing no more than a Momentary Thantafm. 



But whence 'tis that the different Refra- 

 ctive Power of Fluids arifes, is a Problem of 

 the greatefl Moment, and to be rank'd 

 amongft the Secrets of Nature, not yet ob- 

 vious either to our Sences or our Reafonines 

 For pure Water amongft all Fluids \ does 

 leaft of all Refraft the Rays of Light. When 

 tis TwttuSd with Salts difTolved in it, accor- 

 ding to its weight and the quantity of Salt, 

 it increafes the Refradions. And Corrofive 

 Spnts (which are much heavier than Water) 

 do alfo much more Refraft the - Rays of 

 Light: Nor is it any wonder, lince being 

 denfer Bodies, they may eafily be conceived 

 fo much the more to obftrud the paffage of 

 the Rays. But why there mould be fo |reat 

 a Refraction in Burning Spirits and Oils, espe- 

 cially in Spirit of Turpentine, or of Wine, fince 

 they are Fluids extreamly Light in comparifon 

 of Water, and confift very much of fubtie 

 ^therial Particles, does not fo eafily appear - 

 but feems to require (in order to the Expli- 

 cation of it) a more thorough knowledge" of 

 the Nature and Texture of Light. 



But from the difiance (of the Iris from the 

 Sun) given, to find the Ratio of the Refra- 

 dion, is a thing that will give thofe that are 

 curious, an occafion of finding the Refraction 

 of any Fluid, accurately and with little trou- 

 ble^ For if a fmall drop of any tranfparent 

 Fluid, be fuppofed to hang at the bottom of 

 a fmall Glafs Tube, and the Sun being near 

 the Horizon and mining ftrongly, it be ob- 

 ferved under what Angle (with the Point 

 vTh73 :Q D 3 opfofite 



