OF THE WIND AND BAROMETRIC PRESSURE AT BOMBAY. 
17 
appears to be the case with the variations given for Toronto and Falmouth : the double 
rotation is converted into a single one in both instances ; but the rate of rotation is 
decidedly not uniform , being much slower during the night than during the day, 
although the rate during the day is much slower than in low latitudes. Referring to 
the typical curve fig. 9, we see that during the day it rotates through 180° in a little 
over 6 hours ; and from the remarks for St. Helena, it may be inferred that there the 
diurnal wind-curve rotates through the same distance in about the same time, whilst at 
Falmouth and Toronto the curve rotates during the daytime through 180 c in about 9 
hours. At the pole, the curve, as we have supposed it, rotates through 180° in 12 hours. 
20. The results deduced from the curves that have been discussed afford a possible, 
if not a probable, explanation of the observed excess of “ direct ” rotation of the wind- 
vane over “ retrograde ” rotation in the northern hemisphere, and of the opposite excess 
in the southern hemisphere ; and it is one that follows directly from the observed move- 
ments of the wind. They have therefore some relevance in the discussion of storms ; for 
it should be shown that there still remains an excess of direct over retrograde rotation, 
after eliminating the effects of the diurnal variation of the wind, before any allowances 
are made for “ veering ” of the wind in deducing probabilities of the weather from 
observations made at the same hours of successive days ; whilst they show the small mag- 
nitude of allowances that should be made for “ veering” or “backing,” as the case may 
be, in connecting observations that are made at different hours of the day ; and by 
reducing the number of the movements of the vane for which reasons have still to be 
sought, and which would otherwise be misleading, they will increase to some extent the 
value of weather probabilities. Some of the foregoing remarks have been made because 
the writer has observed that, in an “ inquiry into the connexion between strong winds and 
barometric differences ” by the Director of the London Meteorological Office, an allow- 
ance of 45° per day has been made for the “veering” of a strong wind, in deducing the 
probable wind that would follow a certain barometric difference between two stations, 
in accordance with Buys Ballot’s law. The subject appears to be worthy of further 
elucidation, prior to the adoption of daily allowances for “ veering ” in future tentative 
investigations of a similar nature. 
21. In conclusion the writer would say that he makes no pretensions to having framed 
a complete explanation of the diurnal variations of the barometer. In their present 
stage, he regards the notions he has advanced more as providing a working hypothesis 
than as a final solution of the long-vexed question of the barometric tides. As a sug- 
gestion, it supplies in some measure a want that has long been felt, in that it points out 
a definite line of inquiry which cannot fail, if followed, to be productive of most valuable 
results. The fact that the hypothesis undesignedly forms a connexion between two 
meteorological phenomena (viz. the diurnal variation of the barometer and that move- 
ment of the air which Dove has called the “Law of Gyration”) which have hitherto been 
regarded as perfectly independent of each other, and that it simultaneously explains both, 
appears to be in its favour ; and it may be that it contains a germ of truth which, when 
fully developed, will form no small addition to the foundations of meteorological science. 
MDCCCLXXIII. 
D 
