CONFIRMATION OF THE UNDULATO.RY THEOEY. 125 



the refracted ray, would, in this case, guide it from the centre of the 

 surface to every point in the circumference of the circle, and thus make 

 it a cone. This very curious and unexpected result, which Professor 

 Hamilton thus obtained from the theory, his friend Professor Lloyd 

 verified as an experimental fact. We may notice, also, that Professor 

 Lloyd found the light of the conical pencil to be polarized according 

 to a law of an unusual kind ; but one which was easily seen to be in 

 complete accordance with the theory. 



8. Fringes of Shadoivs. The phenomena of the fringes of sha- 

 dows of small holes and groups of holes, which had been the subject 

 of experiment by Fraunhofer, were at a later period carefully observed 

 in a vast variety of cases by M. Schwerd of Spires, and published in a 

 separate work, I7 Beiigungs-erscheinungen (Phenomena of Inflection), 

 1830. In this Treatise, the author has with great industry and skill 

 calculated the integrals which, as we have seen, are requisite in order 

 to trace the consequences of the theory ; and the accordance which 

 he finds between these and the varied and brilliant results of observa- 

 tion is throughout exact. " I shall," says he, in the preface, 18 " prove 

 by the present Treatise, that all inflection-phenomena, through open- 

 ings of any form, size, and arrangement, are not only explained by the 

 undulation-theory, but that they can be represented by analytical ex- 

 pressions, determining the intensity of the light in any point what- 

 ever." And he justly adds, that the undulation-theory accounts for 

 the phenomena of light, as completely as the theory of gravitation 

 does for the facts of the solar system. 



9. Oljections to the Theory. We have hitherto mentioned onlj> 

 cases in which the undulatory theory was either entirely successful in 

 explaining the facts, or at least hypothetically consistent with them and 

 with itself. But other objections were started, and some difficulties 

 were long considered as very embarrassing. Objections were made to 

 the theory by some English experimenters, as Mr. Potter, Mr. Barton, 

 and others. These appeared in scientific journals, and were afterwards 

 answered in similar publications. The objections depended partly on 

 the measure of the intensity of light in the different points of the 

 phenomena (a datum which it is very difficult to obtain with accuracy 



IT 



Die Bcuyunr/s-erschcinunyen, aus dem Fundamental-gesetz der Undulations- 

 Theorie analytisch entwicMt und in Bildern dargestellt, von F. M. Schwerd. 

 Mannheim, 1835. 

 18 Dated Speycr, Aug. 1835. 



