Addenda to Mr. Birt's Report on Atmospheric Waves. 
The following table exhibits the distribution of pressure on the transit of 
the crest of the great wave, Nov. 18, 1842, with especial reference to the 
wave, crest No.4, including St. Petersburgh as a station. 
Tasre XVII. | parom. Phase. Station. Altitude. Wave Phase. 
Min. The Orkneys ... 30°18 
COM ccrnabrt hes ags 30°18 
EWASt. scscecacsee 30°37 Posterior 
Shields {35 .0..08e 30°42 Slope. 
Bristol. sez. cate. 30°42 
Plymouth.....-..« 30-47 
Max. ponege ee beer A < 30°53... | . Crest. 
AUIS: Waadaps aun ae5 30°38 . 
Christiania ...... ig it Nir pecs 
Min. St. Petersburgh.. 29°85 ope: 
A the highest reading at these stations on this day. 
Altitude of anterior slope. St. Petersburgh to London *68 
(A very oblique section.) 
Altitude of posterior slope. Cork to London *35 
(The posterior trough was doubtless some distance north-west of Great Britain and Ireland. 
November 22. Trough between waves 7 and 9.—The trough now trans- 
its St. Petersburgh, crest No. 9 now transits Christiania. We have already 
noticed that crests 7 and 11 were small waves ; abstracting them, we have this 
succession of large waves thus, Nos.1, 3, 5, 9. When crest No.1 traversed 
England on the Ist, its anterior trough extended beyond St. Petersburgh ; 
when crest No.3 traversed England on the 10th, its anterior trough also ex- 
tended beyond St. Petersburgh; when crest No. 5 passed the Orkneys on the 
15th, its anterior trough passed St. Petersburgh; and when crest No. 9 passes 
Christiania (this day), its anterior trough passes St. Petersburgh. These facts 
clearly show the gradual contraction of the waves or oppositely directed beds 
of parallel currents. 
General Conclusion. 
It will be readily apparent from the collation of Mr. Brown’s with the St. 
Petersburgh observations, that the results arrived at in the preceding discus- 
sion have been fully confirmed, and there appears to be but little doubt that 
the waves as determined in the first instance by a discussion of observations 
from the stations announced in my first report (Report, 1844, page 267), and 
further identified and illustrated by the observations collected by Mr. Brown, 
as well as those which have been brought to light by means of Mr. Brown’s 
observations, and confirmed and illustrated by the St. Petersburgh observa- 
tions, had a real existence; an individuality has been attributed to certain 
arrangements of aérial currents and distribution of pressure in connexion 
with such currents, the aggregate pheenomena forming an atmospheric wave. 
Of the waves thus brought to light, two occupy very prominent positions ; 
they stand out as it were from the others; the individuality of each is very 
striking, and the velocities with which they traversed the area isolate them 
from their predecessors and exhibit them not as gregarious, but solitary waves. 
These waves are B° and crest No. 4, the first occurring just previous to the 
setting-in of the great wave, and the last forming its crown. The wave, crest 
No.4, appears from its elevated position on the symmetrical or normal wave, 
admirably adapted to crown our investigations with success, especially in so 
far as its amplitude, velocity and path are concerned, we are now, I appre- 
hend, in possession of materials to determine with a considerable approxima- 
tion to accuracy, these elements. Its longitudinal direction appears to have 
been very extensive. This element would receive considerable elucidation 
by means of observations from the south of France, Spain, Portugal and the 
north of Africa. It is highly probable that this wave in the direction of its 
length stretched from the extreme south to the very north of Europe. 
