166 



REPORT 1839. 



Table XXI. 



Showing the Hours which, either singly or combined, approach 

 the Mean Maxima and Minima Pressures. 



Mean Maximum 

 Pressure. < 



29-8080. 



L 



Hour. 



Single Hours. 



Double Hours. 



8 P.M. 



9 P.M. 



11 P.M. 



10 A.M. 



and 

 10 P.M. 



8 P.M. 



and 

 10 P.M. 



11 P.M. 

 and 



12 P.M. 



11 P.M. 



and 

 8 P.M. 



Deviations 



•0019- 



•0014+ 



•0012+ 



•000 



•000 



•0002 



•0004 



1 



Mean Minimum 

 Pressure. < 

 29-7911. 



Hour. 



3 P.M. 



2 P.M. 



4 P.M. 



4 A.M. 



5 P.M. 



3 A.M. 



4 A.M. 



and 

 4 P.M. 



Deviations 



•0003- 



•0011+ 



•0016- 



•0017+ 



•0027+ 



•0033+ 



•000- 



We may infer from this table that three observations at 

 3 P.M., and again at 8 and 10 p.m., would give us the mean minima 

 and mean maxima pressures very nearly ; consequently the mean 

 pressure and the mean oscillation = -0172, which differs from 

 the true mean oscillation by only '0003 + . The remaining 

 hours may afford approximation by applying corrections ac- 

 cording to the signs. 



I regret that it is not in my power to give the results of any 

 good discussion of the force of the wind for each hour without 

 regard to direction, as I have reason to believe it would throw 

 some light on the phaenomena of the horary oscillation. Thus 

 I have little doubt that the suppression of the morning oscil- 

 lation observed in the months of summer and spring in Plate 3 

 is coincident with the force of the wind, which, from a cursory 

 examination of the indications of Osier's anemometer, appears 

 to be in those seasons greatest at those periods. I hope in a 

 future Report to be enabled to put the Association in possess- 

 ion of some further information on this point. 



The mean hourly observations of pressure are included in 

 Plate 4, with those on temperature, and the dew point, as 

 determined from the indications of the moistened thermometer 

 by Professor Apjohn's formula. The following table contains 

 the Mean Results of the latter for the Years 1837, 18^38, 1839. 



