292 



considerable barometric oscillations observed at Dublin since 

 the beginning- of the present century. 



The greater barometric oscillations at a given place may 

 be considered as the effects of the passage of large atmospheric 

 waves, the direction and velocity of which can be traced by si- 

 multaneous observations made at distant stations. This view, 

 originally propounded by Sir John Herschel, has been con- 

 firmed by Mr. Birt, who has traced with much care and skill the 

 progress of some very remarkable waves over Europe. Much, 

 however, yet remains to be done in connexion with this subject. 

 It is still to be ascertained to which of the two great classes of 

 waves (waves of translation, or waves oi oscillation), the great 

 aerial waves are to be referred ; and it is far from certain, that 

 the dynamical relation between the molecular movement and 

 the phase of the oscillation, which holds in the known forms 

 of waves, will explain the phenomena of the dependence of the 

 wind upon the barometric pressure. 



The chief difficulty in the way of the solution of these 

 questions arises from the fact, that the aerial disturbance is in 

 general the compound effect of the passage of several waves, 

 moving in different directions, and that the phenomena are 

 thus interwoven and complicated. It is, therefore, important, 

 with a view to the disentanglement of their laws, that the cases 

 at first selected for examination should be, as far as possible, 

 free from this complexity. In this point of view, the greater 

 barometric oscillations, in which the principal movement ge- 

 nerally predominates over the subordinate, are especially de- 

 serving of attention ; and on this account, as well as its very 

 unusual nature, the wave of the present month seems to call 

 for the especial consideration of meteorologists. Its complete 

 discussion will, of course, demand the comparison of observa- 

 tions at several stations ; meanwhile the following facts res- 

 pecting it, as observed at Dublin, are given as a contribution 

 to the history of its progress. 



