He also gave reasoning (earlier proposed by Sun Sikong, 1015–1076) that rainbows were formed by the shadow of the sun in rain, occurring when the sun would shine upon it. Paul Dong writes that Shen's explanation of the rainbow as a phenomenon of atmospheric refraction "is basically in accord with modern scientific principles." In Europe, Roger Bacon (1214–1294) was the first to suggest that the colors of the rainbow were caused by the reflection and refraction of sunlight through rain drops.