Captain James on Meteorological Phenomena. 283 



Remarks. 



1. Barometric Pressure. — 



The Maximum height observed was on the 7th 



March, at 9 a.m =30612 



The Minimum height observed was on the 27th 



December, at 9 a.m == 27*895 



Extreme range during the year,...= 2*717 



So great a depression of the barometer has not occurred 

 since January 1839. On the 13th of that month, Mr Adie 

 informs me the height corrected for altitude was 27*53, 

 when, as on the 27th December last, there was a violent 

 storm, which, from observations made, was no doubt a rota- 

 tory storm. The depression observed by Mr Adie was the 

 greatest (as far as I can learn) which has ever been recorded 

 in Edinburgh. 



It will be observed that the mean height of the barometer 

 at 9 A.M., for each month, is higher than the mean height at 

 3 P.M., with the exception of the month of December. This 

 abnormal result was caused by the sudden rise of the baro- 

 meter on the 27th between those hours, amounting to *419, 

 which, on the mean of the month, overpowered the difference 

 due to the influence of temperature at the hours of observa- 

 tion, though it very slightly affected the means for the year. 



It will also be observed that the mean height was greatest 

 in March, closely following the lowest mean temperature of 

 the air, and that the mean height was lowest in August, 

 closely following the highest mean temperature. This fact, 

 coupled with the fact that the barometer is always higher at 

 9 A.M. than at 3 P.M., whilst the temperature of the air is al- 

 ways lower in the morning than in the afternoon, seems to 

 prove that the effect of an increase of temperature, by caus- 

 ing the air to expand and become specifically lighter, pro- 

 duces a corresponding depression in the barometer ; but as 

 the amount of vapour in the air, and the influence of clouds 

 and currents in the upper strata of the atmosphere constantly 

 disturbs the effect of increased or decreased temperature at 



