ATMOSPHEROLOGY. — BAROMETER. 373 



dieted by the barometer. The value of this instru- 

 ment, therefore, in a country where there is fre- 

 quently not an interval of five minutes between the 

 most perfect calm and the most impetuous storm, 

 is almost incalculable. The faithfulness of its in- 

 dications are certainly not sufficiently appreciated, 

 else it would be more generally used. At one pe- 

 riod, I amused myself by registering my predictions, 

 from the changes observed in the barometer ; and on 

 reviewing those memoranda, I find, that of 18 pre- 

 dictions of atmospheric changes in the year 1812, 

 whereof several were remarkable, 16 or 17 proved 

 correct. 



During the whole period in which I have been in 

 the habit of observing the barometer, I have never 

 been able to detect any small periodical changes in- 

 dicative of atmospheric tides. Two remarks, how- 

 ever, I may offer, as being pretty general : That the 

 greatest fall of the mercury is frequently preceded or 

 followed by the greatest rise : And that the same 

 tendency to equality takes place in the pressure, as 

 has been traced in regard of the temperature of the 

 atmosphere ; the mean of the highest and lowest 

 observations in a long series corresponding to a great 

 minuteness with the mean pressure. The former 

 observation will be fovmd frequently to hold, by 

 examination of the series of meterological tables 

 in the Appendix ; and the latter, most particularly, 

 if we refer to the first table of mctcorolocrical re- 



