16 
Accurate absolute values of the barometric dynamical ele- 
ment can, of course, be obtained for those places only where 
hourly observations are made ; but as it appeared to the 
Author that good comparative values w r ould be quite sufficient 
for the general purposes of his inquiry, he decided to confine 
his attention, in the first instance, to oscillations derived from 
observations made once a day only. By this plan the regular 
diurnal oscillations are completely eliminated ; the results are 
adapted for very fair comparison with each other ; and a 
greater number of sets of observations become available for 
the purposes of the inquiry. This method has accordingly 
been employed in the discussion of a very considerable number 
of observations made at various places in Europe and Asia, 
and a table is given showing the mean monthly and annual 
sums of the oscillations of the barometer at seven stations in 
Europe and six in Asia as derived from observations extending 
over periods varying from six to fifteen years. It is, however, 
remarked, with reference to the results given for Greenwich, 
that as the individual observations of each day at Greenwich 
are not given in the published volumes, these results are derived 
from the daily means, and not from single daily observations, 
as in all the other cases. Diagrams of the curves laid down 
from the numbers in this table accompany the Paper. All 
these curves show a principal minimum in one of the three 
summer months, June, July, or August; and in many of them 
there is a second minimum in one of the two winter months, 
January or February. With respect to the two maxima 
which occur between these minima, it is shown that the inter- 
val between their summits gradually increases as we advance 
from the eastern to the western stations. Thus, at Nertchinsk 
(51° 19' N., 119° 3G' E.), the first maximum occurs in the 
middle of April and the second in the second week of Novem- 
ber, the interval being nearly seven months ; at Barnaoul 
(53° 20' N., 83° 57' E.) the first maximum takes place in 
the middle of March and the second in the middle of Novem- 
