The proposition to consider light as rays traveling in straight lines is a scaffold, it is mythology; but this analogy contains a truth, it contains a real building-stone which should not be torn down with the scaffold. This truth is one-sided; it represents one feature of light and disregards other features. It disregards entirely the transversal oscillations of the ether, yet it describes another feature—viz., the transmission and refraction of light for the comprehension of which we need not take into consideration the undulation theory. The physicist calculates with his formula sinα/sinβ = _n_ the angle of refraction. There is certainly neither a sineα nor a sineβ in reality, but there are certain relations of reality which are described in these expressions and the action of the light has a definite quality which can be determined with the assistance of the formula sinα/sinβ = _n_. If the scientist succeeds in determining such real qualities of things, even though it be done with the assistance of mythology, he discovers a truth. He has with the help of his scaffolds succeeded in placing a building-stone where it belongs. Some scaffolds have to be torn down because they hinder further building; other scaffolds must remain because they assist us in modeling, and planning, and predetermining certain processes of nature. They are like staircases which enable us to reach with ease otherwise inaccessible places on towers or domes. * * * * * The idea that science is full of mythology appears strange to the non-scientific, and it is often overlooked by scientists themselves. But the idea that religious mythology in spite of its many irrational superstitions and wrong analogies beams with truth is also little heeded by the many. In fact, man’s method of reaching truth is the same in religion as in science. The religious ideas such as God and soul are mental constructs which copy certain realities; but these very terms, such as they are used, are mythological expressions; they are still surrounded by their scaffolds. Many people know by their own experience the usefulness and indispensability of the scaffold. Without the scaffold they would never have had an inkling of the truth, for the representation of which it was built, and it is natural that they consider the scaffold as the building itself. This is the reason why the narrow-minded orthodox denounce anyone who would lay hand on or tear down any part of the scaffold, which has become a hindrance to the further development of religious ideals. Positivism, i. e. the representation of facts without any admixture of theory or mythology, is an ideal which in its purity perhaps will never be realised. Nevertheless it is no _ignis fatuus_, no will-o’-the-wisp that leads us astray. Our science is constantly more and more approaching this ideal and the progress of humanity is intimately connected with it.