TRANSACTIONS OF THE SECTIONS. 11 



the mode in which the eye acquires its well-known power of accommodating itself to 

 distinct vision at various distances, and the experiments of Troughton and others 

 with a view to determine the question. He then stated that he had ascertained a 

 fact, which he considered to he one distinct step towards the desired explanation, 

 although he must admit that he could not as yet satisfy his own mind with any of 

 the explanations which he had given, nor as yet fully point out how the fact he was 

 about to mention would aid in that explanation. This fact is, that if an object be 

 so placed relatively to the eye as that it is not seen distinctly, distinct vision will be 

 instantly acquired by directing attention to some intermediate object. 



Account of a Series of Experiments on the Polarization of Light by rough 



surfaces, and white dispersing surfaces. 



Bxj Sir David Brewster, F.R.S. L. % E., Hon. M.R.LA. 



These experiments were made with one or more surfaces of ground glass having 

 different degrees of roughness, and upon paper, snow, and white painted bodies. 

 The state of polarization was ascertained by the polariscope with parallel bands, and 

 its amount measured with the polarimeter which he had invented for this purpose. 

 In polarizing light, the atmosphere acts like a rough surface, and hence these experi- 

 ments had an application to that new branch of optical meteorology. The degree 

 of roughness in transparent bodies was ascertained by observing the angle of re- 

 flexion at which a small circular luminous disc of a given intensity either disappeared 

 or began to lose its distinctness of outline. The general effect of roughness of sur- 

 face is to diminish the degree of polarization which would have been produced at the 

 same angle by the surface when smooth. In the case of white dispersing bodies, the 

 intromitted pencil, polarized by refraction, is again reflected, and more or less neu- 

 tralizes the pencil oppositely polarized by reflection. 



On the Nature of the Sound Wave. By J. Scott Russell, F.R.S.E. 



He had determined the existence of certain orders of water-waves governed by dif- 

 ferent laws, and it was necessary, for the explanation of the phaenomena of sound, 

 to determine to which of these orders it was analogous. It was generally supposed 

 that the sound wave was analogous to the waves formed by dropping a stone into 

 the waters of a quiet pool. These were waves of the second order. But his experi- 

 ments had led him to suppose that the sound wave was a wave of the first order, 

 analogous to the wave of translation in water. This determination would effect a 

 considerable change in our conception and explanation of the pheenomena of sound, 

 at present ill understood. For example, the theory of the speaking-trumpet had 

 been given in many forms by different mathematicians ; but it was found that 

 the forms assigned by them were nearly opposite, while their effects were nearly 

 identical. This was just what would result from the theory of the wave of the first 

 order. But the whispering gallery was still more inexplicable on the old theory ; 

 the dome of St. Pauls was an instance — quite inexplicable on the old hypothesis, 

 but his experiments upon it had proved that the wave of sound did in that case 

 obey implicitly the laws of a wave of the first order, and on that theory its phaeno- 

 mena were completely explained. By considering the sound wave as a wave of the 

 first order, it was now easy to determine the principles on which buildings for 

 speaking and hearing should be formed. 



On the Analogy of the Existences or Forces, Light, Heat, Voltaic and ordinary 

 Electricities. By John Goodman, Esq. 



The author enumerates many general properties in which these existences (which 

 term is employed in contradistinction to the opinion frequently received, that caloric, 

 light, &c. are only effects resulting from the motion of material bodies) agree. In 

 reference to the " expansion of metals," in which caloric and the voltaic fluid agree, 

 Mr. Goodman describes apparatus by which he has succeeded in showing expaimon 

 of a column of mercury, by the passage of an electric current through it, while an 

 ordinary thermometer, whose bulb was plunged in the same mercury for an hour. 



