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alſo thereby abstracted, ſo that thoſe Sides ap- peared as diſtinctly outlined as did the Circum- ference of the primary Image Y. so it happens if the Glaſs of the Prilms be free from Veins, and their Sides be accurately plane and well poliſhed while not while not while not Waves or Curles that that that from Sand-holes a bit a bit sprucing with Purty. If the Glaſs be solely well poliſhed and free from Veins and therefore the Sides not accurately plane however a bit umbel-like or concavo-convex, because it oft happens; nevertheless could the 3 Spectrums Y, platinum and platinum need Penumbras, however not in equal diſtances from the Prifms. currently from this need of Pen- umbras, I knew a lot of actually that each one in all the Circles was refraéted in step with in step with regular, uniform, and conſtant law. For if there have been any irregularity within the Refraction, the correct Lines A E and GL that all the Cir- cles within the Spectrum platinum do bit, couldn't by that Refraction be tranſlated into the Lines a e and g las diſtinct and ſtraight as they were before, however there would arife in thoſe tranſlated Lines fome shadow or Crookedneſs or Un- dulation, or different different Perturbation con- trary to what's found by expertise. What- foever shadow or Perturbation fhould be created within the Circles by the croſs Refraction of the ſecond Priſm, all that shadow or Pertur- bation would be confpicuous within the right Lines a e and g one that bit bit Circles. and thus fince there's there's shadow or Perturbation in thoſe right Lines there muſt be none within the Circles. Since the diſtance between
thoſe
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