THE ROYAL IRISH ACADEMY, 1848. 47-> 



That such analogies, and points of correspondence, should exist 

 between the theory of light, and any general theory of vibration in 

 crystalline solids, was, of course, to be expected from the common 

 foundation and the common postulates of the two theories. Not- 

 withstanding this, however, the two theories diverge at a very 

 early point. In both, indeed, the form of the characteristic func- 

 tion is deduced from the assumed molecular constitution of the 

 medium. But that constitution is essentially different in the two 

 cases, the fundamental molecular property of the luminiferous 

 ether, in the theory of Professor M'Cullagh, being the un- 

 changeableness of its density, while the corresponding basis of 

 the theory of Mr. Haughton is the property that the molecules of 

 the medium act on one another in the direction of the joining 

 line.* 



In conclusion, I may observe that the value of Mr. Haughton's 

 theory considered on its physical side, and independently of its 

 mathematical elegance consists in its high degree of generality ; 

 which is such as necessarily to embrace all the fundamental condi- 

 tions of the problem, and thus to leave to future mathematicians 

 the task only of limiting and interpreting his results. 



In speaking of Dr. Hincks' philological researches I must pass 

 over those which relate to Egyptian Hieroglyphics, and hasten to 

 his more recent, and (at the present time) more interesting labours 

 connected with Persepolitan writing. And in order to present an 

 intelligible statement of the nature of these labours, and of the 

 additions which have been thereby made to the existing amount of 

 knowledge upon this curious subject, it will be necessary to take a 

 hurried glance at the history of the investigation, and its principal 

 steps. 



The cuneiform writing has been generally reduced to three 

 leading divisions, which have been denominated, respectively, 

 Persian, Median, and Babylonian. Many of the cuneiform inscrip- 

 tions contain all the three kinds of writing, the first being the 

 principal, and apparently the vernacular record, and the other two 



* The theory of Mr. Haughton bears a much closer resemblance, in many of its re- 

 sults, to the wave-theory of M. Cauchy than to that of Professor M'Cullagh, although 

 it differs from it wholly in method. The theory of M. Cauchy is, in fact, a theory of 

 the laws of propagated vibration in solids, and is inapplicable (as was shown by Pro- 

 fessor M'Cullagh) to light. 



