394 Miscellanies. 



" That there is a striking connection between the barometrical 

 changes, and the variations of temperature. 



" That a relation appears to subsist between the variations before 

 noon, and those before midnight; a great amount of variation before 

 noon being followed, in the same mean day, by a corresponding 

 small variation before midnight, and the contrary. 



" That the season of the year, or the temperature of such season, 

 appears to exercise an influence over the hours of maximum and 

 minimum, and over the amount of mean variations. The minimum 

 and maximum of the morning are earlier, and of the evening later, 

 in summer than in winter. The variations in summer are small at 

 noon, and great about midnight ; those in winter, the reverse. 



" The greatest mean variation occurs in the afternoon, minimum 

 height of the barometer at four o'clock ; and the next greatest, in 

 the forenoon, maximum at ten o'clock. 



" That the general relation between the barometrical changes and 

 the variations of temperature, appears to be direct, during the morn- 

 ing hours, and inverse, during the day and evening." 



These observations have been made with a thermometer attached, 

 and the variations of temperature simultaneously registered with those 

 of the barometrical changes. Mr. Hudson considers the variations 

 of atmospheric pressure to be dependent on temperature, but has not 

 stated any precise ratio by which the changes are regulated ;' nor 

 has he explained any of those circumstances which accelerate or 

 retard the uniform operation of the laws which cause its periodical 

 oscillations. 



The changes of temperature alone appear to be insufficient to ac- 

 count for the phenomena of the barometer. 



There can be no doubt that, comprehending the whole atmos- 

 phere, there is a constant rise and fall, or a great semi-diurnal mo- 

 tion of the air, whereby it is subject to a regular elevation and de- 

 pression twice in twenty four hours, analogous to the tides of the 

 ocean ; and it is well ascertained, that its movements are uniform at 

 the equator, and nearly so through the tropics, while it is subject to 

 great variations and irregularities within the temperate regions. 

 These changes might be ascribed to the extremes of temperature in 

 extra-tropical climates, were it not that barometers, which have been 

 simultaneously observed in various and distant countries, rise and fall 

 together; and it is seen, by Mr. Hudson's observations, that temper- 

 ature cannot be the only disturbing influence, because the barometri- 



