25 



Mr. Petrie exhibited a MS. of the four Gospels, in Latin, 

 of which he had given an account in a paper read some time 

 since before the Academy. This manuscript is said to have 

 been that given by St. Patrick to the first Bishop of Clogher. 

 It is enclosed in a brazen case, of very curious workmanship, 

 on which the circumstances connected with the gift are re- 

 presented in highly raised figures. 



Professor Lloyd communicated to the Academy the con- 

 tinuation of his investigations " On the Propagation of Light 

 in uncrystallized Media." 



In the first part of this paper, read on a former evening, 

 the author had expressed his conviction that the problem of 

 wave-propagation in bodies was incompletely solved, unless 

 the action of the material molecules be taken into account. 

 This he has attempted to do in the present continuation, 

 confining himself to the comparatively simple case in which 

 the molecules of the ether and of the body are uniformly 

 diffused. 



The differential equations of motion inferred from these 

 considerations contain, each, the displacements of the mole- 

 cules of the ether and of the body, — with coefficients depending 

 on the masses and distances of the molecules, the law of force 

 to which they are subjected, and the length of the wave. 

 By a particular method of elimination, these pairs of simul- 

 taneous equations may be reduced each to a single one, of 

 the simple form which occurs in the case of a single vibrating 

 medium, the new coefficient being connected with those of 

 the original equations by an equation of the second degree. 

 The expression for the displacement, then, is of the same 

 form as in the case of a single vibrating medium; but 

 the relation between the coefficients of the time and of the 

 distance, and consequently the velocity of propagation, will 

 be very different. 



