the Imperial Academy of Sciences at St Fetersburg. 81 



for each month are given. Since 1781, the thermometer has 

 been observed morning and afternoon of each day, at what 

 precise hour is not said : it appears that the hours of observa- 

 tion vpere not always the same. 



" Since 1803, the meteorological observations of St Peters- 

 burg present more regularity. Observations are made three 

 \imes a-day, mox'ning, afternoon, and evening ; the direction 

 of the winds each day is noted. But it is especially since 

 1822 that we possess good meteorological observations ; since 

 that period, their execution has been confided to the acade- 

 mician M. Wisniewsky. The thermometer, the barometer, 

 the direction of the winds, and the state of the weather, are 

 regularly observed thrice a-day, at 7 o'clock in the morning, 

 2 in the afternoon, and 9 in the evening. The quantity of rain 

 and snow is also marked. Tlie acknowledged ability of the ob- 

 server guarantees the accuracy of the observations: no precau- 

 tion has been omitted, no interruption has taken place. It is un- 

 doubtedly a matter of regret, that other occupations have not al- 

 lowed M. Wisniewsky to observe more frequently ; three observa- 

 tions a-day, executed at hours which do not coincide with those 

 of the minima and maxima, are not sufficient to determine with 

 exactness the horary variations of the bax'ometer, an object 

 which, for some time, has fixed the attention of natural phi- 

 losophers, and "with which so many distinguished observers 

 are almost exclusively occupied. To know exactly the daily 

 gradation of temperature, a greater number of observers would 

 be necessary ; it would be necessary at least to obsei've the 

 minimum of each day. No hygrometrical observations have 

 been made ; the hygrometer of Saussure, the most exact of 

 those that were known when the observations began, and, con- 

 sequently, the only one which could well be employed, is too 

 uncertain in its indications, and too easily deranged. Never- 

 theless, notwithstanding these defects, the observations of M. 

 Wisniewsky present so complete a summary, and offer so exact 

 a table of the climate of St Petersbui'g, that I believe I shall 

 render an important service to science by publishing them in 

 all their details, after I have calculated them according to the 

 rules generally admitted. I publish them in all their details, 



VOL. XXVIII. NO, LV. JANliARY 1840. F 



