According to the observations of experimental science, the blue sky which stretches above us is not a world of bliss, but an optical illusion due to the refraction of light by the atmosphere and from this point of view it is obviously right to maintain that the home of the blessed does not lie up there. Nevertheless it would be a great mistake to assert that the association of ideas between the visible heavens and the celestial Paradise does not arise from the nature of things, but rather from ignorance and ingenuousness mixed with imagination and sentimentality; for the blue sky is a direct and therefore adequate symbol of the higher and supersensory degrees of Existence; it is indeed a distant reverberation of those degrees and it is necessarily so since it is truly a symbol consecrated by the Sacred Scriptures and by the unanimous intuition of peoples...The fact that the symbol itself may be no more than an optical illusion in no way impairs its precision or efficacy, for all appearances, including those of space and of the galaxies, are strictly speaking only illusions created by relativity.