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XV. Reduction of Anemograms taken at the Armagh Observatory in the Years 
1857-63. By T. R. Robinson, D.D., F.R.S., F.A.S., &c. 
Received June 11, 1875, — Read June 17, 1875. 
In the beginning of the year 1845 I erected a self-recording anemometer at the Armagh 
Observatory, and have a series of its records np to the present time, unbroken except by 
accidents to the apparatus or occasional illness of the observers. I, however, soon 
found it was impossible for me and my single assistant to reduce continuously the mass 
of materials which was accumulating, without neglecting the primary objects of the 
establishment ; and I was obliged to content myself with preserving them, in hope that 
they might be available to future inquirers. It was thought, however, by some distin- 
guished members of the Royal Society that it was desirable to ascertain how far such 
observations are able to develop any definite laws amid the seeming lawlessness of the 
wind ; and a grant was made to me from the Government Grant sufficient to discuss the 
anemograms for the seven years from 1857 to 1863. The work has been long delayed 
by the death of one of the computers, the migration of another to India, and my own 
temporary blindness. 
The anemograph is that described by me in the 4 Transactions of the Royal Irish 
Academy,’ vol. xxii. It differs in nothing essential from that employed by the Meteo- 
rological Committee of the Royal Society : the recording-apparatus is different, and the 
direction is observed by a vane whose excursions are controlled by a peculiar contrivance 
instead of by a windmill. The space-records were read to 0-25 of a mile (statute), and 
the directions to 0 o- 5. The S. and W. components of the hourly velocity were computed 
for each to two places of decimals. 
Wind is caused by a difference of pressure in the air over adjacent portions of the 
earth’s surface ; but of the agencies which produce this difference we as yet are imper- 
fectly informed. Heat is obviously a most important one. We see that the action of 
the sun must produce a current from polar towards equatorial regions, and that when 
the geographical conditions of districts not too far asunder are such as to make their 
temperatures unequal, air-currents between them will result. The changes of solar 
action at a given place depending on the hour of the day am) the day of the year, ought 
to produce definite periodical modifications of the wind ; and the currents due to the 
varying tension of aqueous vapour ought to be similarly periodical. Were these the 
only causes of the wind, there seems no reason why its force and direction at a given 
time and place might not be predicted as certainly as the sun’s altitude. But there are 
evidently disturbing agencies of great power which entirely mask the regular course of 
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