Up to some seventy years ago Descartes' view of the formation of the rainbow was universally accepted. In i836 the English astronomer Airy published a new theory, but, as it often happens, it found few admirers, some admitting it only for the explanation of the so-called supernumerary bows. Of late years, however, several scholars have endeavored again to draw the attention of scientists to Airy's theory; as prominent among them may be mentioned Messrs. Mascart and Pernter.
Why, then, one might ask, is Airy's theory so little known whilst that of Descartes is almost universally taught ? The reason may be found in the difficult calculations requisite for a full understanding of Airy's theory. If, therefore, it cannot, to a sufficient degree at least, be brought within the reach of non-experts in physics and higher mathematics, no one will require of our colleges and text-books to pay much attention to it. But this is not the case. In his "Ein Versuch, der richtigen Theorie des Regenbogens Eingang in die Mittelschulen zu verschaffen," Mr. Pernter succeeded in putting it into such form that it may without difficulty be introduced into high-schools and colleges.
In this essay we shall strive for the same end; our material is drawn from Mr. "Pernter's writings on this subject.*
In order to show the differences between the two theories, we first give a short account of that of Descartes.
* " Ein Versuch, der richtigen Theorie des Regenbogens Ei~gang in die Mittelschulen zu versehaffen," "Neues fiber den Regenbogen" and "Die Farben des Regenbogens." Dr. J. M. Pernter is Professor at the University of Vienna (Austria) ; he is acknowledged as an authority in meteorology.