18 



The foregoing table of the daily mean heights of the 

 barometer for Greenwich for every day of the year is the 

 result of thirty years' observations made in one locality, 

 and, with few exceptions for so long a period, by one 

 person. The instrument by which the greater number 

 were registered is by Watkins and Hill, the tube of which 

 has a bore y 6 ^ths of an inch in diameter. The table is 

 original, and it may assist in confirming that, at certain 

 seasons of the year, great periodic atmospheric maxima 

 and minima take place. The greatest daily mean pressure 

 for the year, which a consecutive five years' observations 

 will not only verify but increase, occurs about the 9th 

 of January, and the minimum daily mean depression 

 towards the end of November. It is a remarkable co- 

 incidence, that the lowest daily mean temperature for 

 thirty years occurs on the 8th and 9th of January, and 

 the daily mean temperature for November rises suddenly 

 four degrees in the last few days in November. 



The greatest monthly mean pressure occurs in June, 

 and the lowest in November. 



From June the monthly mean pressure declines till 

 November, when it again rises and attains a second 

 maximum in January ; and again falling, comes to its 

 second minimum in March. 



The mean annual pressure for noon at Greenwich is 

 29-872 inches. 



