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 would 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 tlie 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° 36^ E.), the first maximum occurs in the 

 middle of April and the second in the second week of Novem- 

 ber, the interval being nearly severi 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- 



