Variation of the Barometer at Paris. 



73 



till 3 h p. m. From this epoch it rises again, reaches its second 

 maximum at 9 h p. m., and falls a second time, in order to ex- 

 hibit on the following day the same fluctuations. The excess 

 of the greatest height, which takes place at 9 h a. m., above the 

 smallest, which takes place at 3 h p. m., indicates the extent of 

 this atmospherical tide at the place where the observation is 

 made. But in order to obtain that value, the observations of 

 several years are necessary. 



The general result of these observations, reduced to the 

 zero of temperature, * are as follows — 



Mean ot eleven 



years, from 

 1816 to 1827- 



January, 



February, 



March, 



April, 



May, 



June, 



July, 



August, 



September, 



October, 



November, 



December, 



Mean, 



tfh a. m. November, 



_ 



ram. 



779757,429 



757, 



757,868 757,236 757,557 0,929 



758,106 



758,165 



756,203755,98775 



755,253754 



755,253754 



757,307 



756,554 



756,807756 



756,773 



754,772754 



755,822755,700755 



755,152 



,881 



,991 

 757,084 

 756, 



,492 

 756,421 



,547 



755,009 



3h P. M. 



174755 



756,347 756,078 755,591 75/y,950|0,756 0,373 



B* 



757,6900,6770,261 



57,5570,9290,321 



5,406 755,823 0,797 0,500 



754,243 754,780 1,010 0,537 



754,440 754,786 0,813 0,346 



756,600 756,875 0,707 0,275 



,817756,1400,7370,323 



755,953 756,271 0,854 0,318 



755,972756,4320,801 0,460 



754,021 754,5220,751 0,501 



,277755,6600,545 0,383 



754,703 754,950 0,4 49 0,24? 



First 

 period. 



Second 

 period. 



This table contains the mean heights of the barometer for 

 the different months of the year for eleven years, from 1816 — 

 1826, at the epochs of the daily periods. This arrangement 

 of the results shows not only the differences in the heights 

 which exist at different hours of the day, but also those which 

 take place every month at the same hours. Hence it appears, 

 as M. Ramond long ago remarked, that the selection of the 

 hours and the months of observation ought not to be a matter 

 of indifference, when we wish to determine the mean pressure 

 of the atmosphere at a given place. 



* In making this reduction, M. Bouvard has followed M. Ramond in 

 correcting the mean monthly heights of the barometer by the mean height 

 of the thermometer for the same month. This method is much less labo- 

 rious than that of correcting each observation. 



