404 
DE. T. E. EOBINSON ON THE SEDUCTION OE ANEMOGEAMS. 
the phenomena, and of whose nature we can only form vague conjectures. The accu- 
mulation of ice in the polar regions forming icebergs may be such an influence ; and 
what we have learned recently of the action of the larger planets on the solar spots, 
and of the connexion of the development of those spots with the magnetic storms and 
auroral discharges of our own planet, may suggest the possibility of extra-terrestrial 
forces playing some part in the question before us. But without following in the track 
of imagination, this is certain, that however complicated and irregular a phenomenon 
may be, if we have a sufficient number of observations, it is possible to determine the 
values and periods of those parts of it which are subject to definite laws. Where any 
of these periods agree with those of agents whose influence is certain, they may be 
referred to them with certainty, and their effect eliminated, making it much easier to 
deal with the residual phenomena. 
In the present instance the want of self-recording instruments for pressure, tempera- 
ture, and vapour-tension compelled me to consider the wind solely in reference to time, 
as depending on the hour of the day and on the month ; and even with this simplifica- 
tion it is not easy to come to precise results. Were we to seek a velocity and direction 
which might be considered normal for each hour of the year, such is the irregularity of 
the air-currents, that I think it could scarcely be obtained in less than 100 years. Even 
if we confine ourselves to the west and south components, and take for successive hours 
the mean of the seven years concerned, it differs so widely from the means of the pre- 
ceding and following hours, that any existence of law might seem impossible. But if 
the hour-means be taken for 20 or 30 successive days, their means present a very 
different aspect. I have taken them for months. 
Before dealing with these components, I think it may be instructive to present a 
Table giving a synoptic view of the winds, which may show their general character at 
Armagh during the seven years concerned. It gives for each month and for each 
octant of the horizon (S. to S.W., S.W. to W., &c.) the mean hourly velocity, the mean 
direction, and the approximate number of hours during which this wind has blown. 
At the end of each month is given the maximum hourly velocity for each year, the 
number of hours when the velocity exceeded 25 miles, and the number of hours during 
which the anemograph has recorded 0. This does not imply that during this time there 
was no wind, but that there was not enough to move the instrument. This requires a 
velocity =l m - 74. 
The direction-vane is much more sensitive (very much more so than the windmill- 
apparatus now used to record the direction), and therefore the records of direction are 
more numerous than those of velocity. 
