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. 
Tt 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. 
