156 



RKPORT— 1839. 



14. Although the times of the horary semi-oscillations in the 

 different seasons, as shown in Plates V. and VI., are equal, or 

 nearly so, yet the oscillations themselves are unequal, as in the 

 former instances for each year delineated in Plate V. ; the as- 

 cent in the evening generally exceeding the ascent in the morn- 

 ing, except in the period of the three months of winter laid 

 down in Plate VII., when the reverse appears to be the case, 

 a circumstance by no means unworthy of notice. 



The difference in the amount of the morning and evening 

 waves, as shown in Plate VII., is greatest in summer and 

 spring, and least in autumn and winter. 



15. Supposing, as before, the daily march of the pressure to 

 consist of two complete waves, extending through periods of 

 twelve hours each, then the comparative amount of these may 

 be seen in the three following tables : 



Table IX. 



Showing the Mean Morning and Evening Oscillation in the 

 Years 1837, 1838, 1839, with their Differences from the Mean 

 of each year ; together with the Difference of the Morning 

 and Evening Mean Oscillations. 



Years. 



Mean Oscill. 



of 



Year. 



A.M. 



P.M. 



Difference 



of 



Morning and 



Evening. 



Oscillation. 



Difference. 



Oscillation. 



Difference, 



1837 



1838 

 1839 



•0180 

 •0164 

 •0162 



•0150 

 •0164 

 •0146 



•003- 

 •001- 

 •0016- 



•0210 

 •0174 

 •0179 



•003+ 

 •001 + 

 •0016+ 



•0060 

 •0020 

 •0033 



Mean ... 



•0168 



•015 



•0018- 



•0187 



•0018+ 



•0038 



Table X. 

 Showing the Mean Morning and Evening Oscillation of Sum- 

 mer and Winter in Periods of Six Months each, with their 

 Differences from the Mean Oscillation of each Season, and of 

 the Year; also the Differences of the Morning and Evening 

 Mean Oscillations. 



Seasons. 



1 . 



r 



..M. 



1 



Diflferences 



of 



A.M. & P.M. 



1 



Differences. 



1 



Differences. 



Season. 



Year. 



Season. 



Year. 



Summer . 

 Winter... 



•015 

 •020 



•0125 

 •0175 



•0025- 

 •0025- 



•0043- 

 •0006 



•0175 

 •0225 



•0025+ 

 •0025 + 



•0026+ 

 •0056+ 



•005 

 •005 



