Barometric Wave, November 184'7. 41 



points, as we have before ob«ei ved, being thrown higher than 

 others with which they were on a level. This displacement 

 presents very regular gradations, and may be considered as 

 corresponding to the deviations from totality or annularity 

 observed during the progress of a solar eclipse at stations 

 removed from the line at which it is central. The further the 

 observer is situated from the central line, the smaller the eclipse, 

 and the greater the deviation either from totality or annularity. 

 In like manner, the further the observer is removed from the 

 line of greatest sijmmctri/ of the barometric wave, the greater 

 will be the deviations from symmetry in the curve representing 

 the observations. The analogy just noticed not only holds 

 good for one eclipse and one barometric wave, but as the same 

 eclipse presents at the same stations different phases on the 

 occasions of its successive returns, sometimes a[)pearing only 

 as a slight obscuration of the solar disc, at others as a great 

 and central eclipse, so the barometric wave presents a different 

 phase on each of its returns ; the curve representing the ob- 

 servations during its transit exhibits a differentybr/rt, the sym- 

 metrical arrangement of its parts constituting its distinguishing 

 characteristic*. From the assemblage of curves representing 

 the great symmetrical wave on its successive returns, the lines 

 of greatest symmetry appertaining to each return may be de- 

 termined, and from these the mea7i. line of greatest symmetry 

 may be traced over Europe. It will be more difficult to trace 

 in connexion with this line mean lines of deviation on each 

 side, owing to the erratic character of the subordinate waves 

 forming the inflexions of the symmetrical curve ; but this may 

 be done with great ease on the occasion of each successive 

 return, provided there are a sufficient number of stations of 

 observation judiciously placed over the surface of Europe, 

 from which such a chart may be constructed. In the present 

 instance we may take the two apices of the 10th and 18th. It 

 is highly probable that at some station to the south-east of 

 London both attained the same altitude: this station would be 

 at least near to, if it was not, the station of greatest symmetr}'. 

 The departure from symmetry would not only be indicated, 

 but the numerical value of it given by the depression of one 

 apex below the other. Thus at London this value is "051 ; 

 but at Weston in Somersetshire it is "IGl, and at Halifax in 

 Yorkshire it appears to be '250 ; and there is very little doubt 

 that it will be found to increase, especially towards the north- 

 west. When these values of deviation from symmetry are 

 determined year after year, and combined so as to obtain the 



* IJy referring to tiic [)haeiiOiiiena of a solar eclipse us analogous to those 

 i>t a baroiiictrif wave, it is not intended to convey tlic idea tiiat tiiere is 

 any neccbbary connexion between them. 



