ON ATMOSPHERIC WAVES. 133 
ing problem of the barometric oscillations,—one class of philosophers re- 
garding them as only the effects of currents of air of unequal temperature 
and moisture; and another as the effects of undulations progressing in the 
manner of waves of sound, and propagating themselves with great velocity over 
large portions of the earth’s surface (Report, 1845, page 30). 
It is not my intention to enter into an examination of the conclusions and 
results which Mr. Brown has arrived at; as the question is open, I apprehend 
I shall not be doing an injustice to that gentleman by employing a rather 
different process to that which he has used, and further discussing the ob- 
servations he has given. I beg to acknowledge the obligations I am under 
to him for these observations, and especially for the plates, of which I have 
before spoken: they are extremely interesting in the present inquiry. 
In accordance with these remarks, I shall select the following stations from 
Mr. Brown’s list:—the Orkneys, Belfast, Shields, Cork, Bristol, Plymouth, 
London, Paris, and Christiania. The reason I have omitted Glasgow and 
Armagh will be apparent from Mr. Brown’s notes. As I intend to discuss 
these observations with especial reference to the wave hypothesis, I shall 
most cautiously avoid in my future remarks any thing that may at all bear 
on Mr. Brown’s views. The plan I intend to proceed on is as follows. I 
shall select the middle observation of each day ; at those stations where only 
two are given morning and evening; I shall take a mean of them. These 
observations I shall so arrange that they may exhibit the distribution of 
pressure over the area for each day—the line or lines of the greatest diminu- 
tion of pressure—and the relation of such distribution and of such lines to 
the aérial currents or winds. As a convenient method of readily expressing 
these various relations and giving to the discussion that completeness which 
otherwise it would want, I shall adopt the wave hypothesis, and to every line 
of barometric maxima apply the term crest and to every line of minima the 
term trough. Ina word, I shall regard the progress of the barometric and 
anemonal phenomena as the progress of waves. The observations will re- 
main the same both in Mr. Brown’s and my own discussions, the results only 
will be different ; and it will remain for other philosophers, by more closely 
investigating the subject, and submitting the observations to a more rigorous 
and searching discussion, to advance this interesting inquiry and to become 
more intimately acquainted with the causes of these interesting phenomena. 
Having announced my intention of discussing these observations on the 
wave hypothesis, it will be important before commencing such discussion to 
supply a deficiency in my two former reports, and endeavour to give a com- 
pleteness to them which at present they are destitute of. ‘The nature of the 
inquiry occasioned them to be drawn up and presented to the Association in 
a fragmentary manner, the first detailing the steps I intended to adopt in the * 
examination of the great wave of Nov. 1842, and the second the further in- 
formation I had obtained relative to this and other atmospheric undulatory 
movements ; and to a certain extent the same remark will apply to the present 
report, embodying as it does the progress made since the last meeting of the 
Association. The deficiency to which I allude is the notion we form of an 
atmospheric wave ; I shall therefore, previous to placing the discussion of Mr. 
Brown’s observations before you, as clearly as I can, state the idea I entertain 
of such a wave, and in introducing it to your attention I shall avail myself of 
Mr. Scott Russell’s designation of the elements of a wave as in figure 1, and 
then proceed with the definition of an atmospheric wave. 
