Another beautiful grotto has green instead of blue refractions; the effect in both cases is due to the light entering by a small entrance. [Please select]
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Moreover, apart from illusory refractions, of which there is no question here, the indications of light are precise; one goes straight to the object seen. [Please select]
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By these two refractions, and this single reflection, the light is sent to the eye of an observer facing the drop, and with his back to the sun. [Please select]
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