496 ADDRESS DELIVERED BEFORE THE BRITISH ASSOCIATION 



the objects with which the science is concerned, and an investiga- 

 tion of causes as well as laics of phenomena. 



It may be admitted, at once, in reference to this objection, that 

 the physical constitution of the bodies whose changes we are inves- 

 tigating is a proper object of study to the physicist ; but it does 

 not seem to follow that it should necessarily be conducted by the 

 same individuals who are in search for the laws of the phenomena, 

 or even that the former knowledge is essential to the progress of 

 the latter. The noblest of all the physical sciences, Astronomy, 

 is little more than a science of laics laws, too, of the simplest kind 

 of change ; and the knowledge of these laws is wholly independent 

 of the physical constitution of the masses whose movements it studies. 

 A similar observation maybe made regarding the science of Terres- 

 trial Magnetism ; and the case is one which brings us still nearer 

 to the question at issue, inasmuch as the laws which have been 

 obtained and they are numerous have resulted from a method 

 of inquiry altogether similar to that adopted in Meteorology. 



Time will not permit me to inquire whether there is not a 

 misconception of a metaphysical kind at the root of this objection. 

 I may observe, however, before leaving the subject, that there are 

 two modes of studying the sequences of natural phenomena, one 

 in their relation to time, and which is best accomplished by obser- 

 vations at stated periods, and the other in the relation of the 

 successive phases of the phenomena to one another. Of these, the 

 latter, although not wholly neglected, has not been so much 

 followed as it deserves ; and I cannot but think that it would, 

 if more systematically followed, enrich the science of Meteorology 

 with a new harvest of results. 



The most important of the recent additions to the theory of 

 Light have been those made by M. Jamin. It has been long 

 known that metals differed from transparent bodies, in their 

 action on light, in this, that plane-polarized light reflected from 

 their surfaces became elliptically-polarized ; and the phenomenon 

 is explained, on the principles of the wave-theory, by the assump- 

 tion that the vibration of the ether undergoes a change of phase at 

 the instant of reflexion, the amount of which is dependent on its. 

 direction, and on the angle of incidence. This supposed distinc- 

 tion, however, was soon found not to be absolute. Mr. Airy 

 showed that diamond reflected light in a manner similar to metals ; 



