@rag7) 
XIX.—On the Diurnal Oscillations of the Barometer. Part I. By ALEx- 
ANDER Bucuan, Secretary of the Scottish Meteorological Society. (Plate 
XXXIIT.) 
(Read 15th March 1875.) 
Of the periodical variations of atmospheric pressure the best marked are 
the diurnal oscillations which in tropical and sub-tropical regions are among the 
most regular of recurring phenomena. In higher latitudes these oscillations 
become from day to day gradually more and more masked, owing to the 
frequent fluctuations to which atmospheric pressure is there subjected. If, 
however, hourly observations continue to be regularly made for some time, the 
diurnal oscillation becomes apparent in the averages deduced from them. 
At Edinburgh, where observations were made at 9.30 a.m. and 3.30 P.M. 
during 109 months, the morning exceeded the afternoon means in every one of 
the months except six, and on these six occasions the barometric phenomena 
were similarly abnormal at neighbouring stations. Thus the oscillation 
between these hours occurs with very considerable regularity at Edinburgh ; 
but at stations in north-western Europe more under the influence of the ocean, 
such as Guernsey, Helston, Valentia, Helder, and Copenhagen, though situated 
in lower latitudes, it is much less regularly marked. In the course of this 
investigation all clearly abnormal, or otherwise doubtful means were, when- 
ever possible, inquired into, with the result that in most cases they were 
due to errors of observation of an inch or half an inch; to errors arising 
from including very high or low readings in the averages of one hour, while 
observations on the same day were wanting for the other hour ; and lastly, to 
clerical and printers’ errors. All means evidently erroneous have been rejected. 
The general character of the daily oscillations of atmospheric pressure is 
shown by the two curves of the accompanying figure, which represent by the 
Inch. 
-+0:060 

line that at Vienna for ten years. 
VOL. XXVII. PART II. 5 M 
