124 REPORT—1846. 
reason to believe that it had again returned and that its fourth transit had been 
observed. Between these epochs, Nov. 6 and 21, all its essential features were 
exhibited. The large central undulation, also forming the crown of the great 
wave and occupying in this instance five days, was very distinctly marked ; 
and the two smaller undulations on each side the central wave, making with 
it the five of which the great wave is composed, were also well-developed. 
These smaller waves did not appear to co-ordinate with those of former 
transits. The great wave culminated on the 14th. 
Corresponding barometric movements. 
Crest. 
1842. November 11 to November 25. Nov. 18. 
1843. November 6 to November 21. Nov. 14. 
1844. October 20to November 4. Oct. 27. 
1845. November 6 to November 21. Nov. 14. 
VI. The movements between the above epochs in each year were more or 
less symmetrical, the axes occurring on the dates indicating the passage of 
the crests. In the year 1845 the symmetrical movements appeared to extend * 
greatly beyond the limits noticed above, for not only did the central undula- 
tion which culminated on the 14th form the axis of the great wave (properly 
so called), but also of a system a¢ least double its extent, namely from Oct. 29 
to Nov. 28. Observations received from Hastings appear to indicate that 
the barometric oscillations during October, November and December were 
symmetrical, the axis occurring about the middle of November. 
VII. In my last report (Report, 1845, page 116) I stated that the mini- 
muni of the 16th of Feb. and that of the 5th of Oct. in the year 1841, formed 
the limits of the period of least range for that year. It is well known that 
the barometric oscillations are divisible into éwo classes ; those of small range, 
confined to the swmmer half year; and those of great range, the period of 
their development being the winter. These greater oscillations begin to appear 
in October. Fig. 2, Plate I. (Report, 1843) exhibits a similar undulation 
to that of Sept. ]4 to Oct. 1, 1842, of seventeen days’ interval with wo sub- 
ordinate maxima interposed. The depression of the 23rd was very considera- 
ble, and rendered memorable by the inundation of the Madeiras. We ac- 
cordingly find that the larger undulations began to appear in these latitudes 
in 1842, about the 16th of Oct. The seventeen-day undulation, Sept. 14 to 
Oct. 1, occurring about a fortnight later in 1845, brought it within the period — 
of the commencement of the greater secondary undulations, and we find it 
interrupted by ¢wo very remarkable waves, in both cases rising above the 
general surface of the normal wave. On comparing the curve from Oct. 1 to 
17, 1845, with that of Oct. 15 to 31, 1842, and bringing the minima in both 
cases on the same vertical line, but little if any resemblance can be traced 
between them. There are however these interesting exceptions. During — 
the first seven and a half days the descent in each case is interrupted by a — 
superposed wave, the co-ordinates of that of 1842, being about double those of — 
the superposed wave of 1845. The ascent during the succeeding seven and 
a half days is also interrupted in each case by superposed waves, but the 
characters of them are reversed, the largest occurring in 1845 and the smallest — 
in 1842; the relations are nearly similar to those characterizing the super- 
posed waves of the descent, that of 1845 being nearly double that of 1842. — 
Another most remarkable circumstance is also apparent on the comparison — 
of these curves, the displacement of the maxima of these superposed waves, 
or the interval between their crests. It is probable that three waves transited 
during the seventeen-day undulation, Oct. 14 to 31, 1842, having their re- 
spective maxima on the 21st, 25th, and 27th; there are also traces of three _ 
