ON ATMOSPHERIC WAVES. 269 



true character of the depression. The result of this portion of my investiga- 

 tion is, that during the 8th and 9th of November tivo systems of waves were 

 traversing the British Isles and the neighbouring parts of Europe, the largest 

 from the N.W. and the smallest from the S.S.W. A trough belonging to the 

 largest system extended from Scilly to Longstone, or, as shown by the model, 

 in a line to the S.E. of this. A well-marked wave of the second system 

 passed over on the 9th from Scilly to Longstone ; the altitude varied accord- 

 ing to the disposition of the atmosphere arising from the first "w^ave from 

 29*537 at Bardsey to 29*590 at Longstone*. From a very careful examina- 

 tion of the passage of this wave over the area, it appears that its transverse 

 section extended over 341 miles with an altitude of '090 inch. This wave 

 progressed at the rate of twenty-five miles per hour. The great depression 

 from Geneva to Longstone appears to be connected with, or result from, a 

 permanent depression in the north-west of England, or a gradual diminution 

 of pressure from the central part of Europe ; and it is probable that the nodal 

 character of Brussels may depend on its enjoying permanently a greater 

 pressure than the stations to the north-west of it, and that it is only very high 

 waves, such as that of the 18th November, that are capable of depi'essing 

 Brussels below stations situated in the atmospheric valley, as Dublin. It is 

 remarkable, that in all large storms the barometer is more depressed in the 

 central part of England. It appears that the maximum, or the apex of the 

 wave succeeding the trough of the first system, was comparatively small, ap- 

 pearing only as a bulge on the posterior slope of a large wave. This however 

 will be better determined by the further examination of the curves. 



I apprehend I have thus obtained a starting-point from which the true 

 character of the wave or waves from the llth to the 25th November may be 

 determined, and the agreement or anomalies of the curves explained. I have 

 accompanied this communication with specimens of the tables I intend to 

 construct, the diagrams of the areas (these are at present imperfect, owing to 

 all the stations not having been inserted), models to assist in obtaining an idea 

 of the disposition of the atmosphere, sections of the waves projected from 

 observations reduced to the level of the sea, and the projected curves with 

 the spaces betvveen them coloured as before mentioned. I shall endeavour to 

 execute, by the meeting of the Association, the continuation of these and 

 other curves past the depression of the llth, with their appropriate colours; 

 but I fear I shall not be able to obtain any further results by that time than 

 those already mentioned in this communication. I have also inclosed copies 

 of remarks I have made with a view to explain the drawings and models, and 

 to illustrate the manner in which I pursue the inquiry. 



These remarks and explanations I do not by any means consider in the 

 present state of the inquiry as final ; 1 have used them merely to assist in ob- 

 taining an idea of the nature of the barometric fluctuations within the area 

 and at the times named, with the view of clearly understanding the nature of 

 the great depression of the 1 1th. You will perceive 1 have scarcely touched 

 on any of the continental stations ; and as I more fully investigate their curves 

 and sections, many of the views recorded in the remarks, &c. will doubtless 

 require modification. I am inclined however to consider the two systems as 

 clearly made out, and that the form, direction, and velocity of wave B 1 has 

 been tolerably well apprehended. I have left blank leaves in writing the re- 

 marks and explanations, for any notes or suggestions you may feel desirous of 

 inserting. 



You will probably notice the progress I have made, or rather the plan I 

 * At Scilly the altitude of the maximum was 29"645. 



