719 



that the barometric variations were subject to 

 certain laws. Van Swinden announced in the 

 year 1776, the existence of a diurnal period : he 

 employed the method of the mean, to exclude 

 the effects of accidental perturbations ; but he 

 fixed hours for the maxima and minima ( + lh h ; 

 — 6 U ; -f 10 h ; — 22 h astronomic time), which, ac- 

 cording to the position of Franecker, and the 

 analogy of the observations of Koenigsberg, ap- 

 pear little probable. Cotte # Hemmer, Planer, 

 and other members of the Meteorologic Society 

 of Manheim, asceriained that the passage of the 

 Sun over the meridian, tended to make the ba- 

 rometer descend, and that that instrument was 

 generally lower at 2^ in the afternoon, than in 

 the morning and evening. Due la Chapelle 

 carefully observed the more or less swelled con- 

 vexity of the column of mercury, and conclud- 

 ed from his labors, that the barometer lowers in 

 the south of France, from 7h in the morning till 

 2|ii in the afternoon ; that it rises till 10i h in the 

 evening, and again descends rapidly during the 

 night. All these assertions were vague and con- 

 tradictory: the first precise observations made in 

 Europe on the horary variations of the barome- 

 ter, were by M. Ramond. " I obtained," says 

 that excellent observer -f-, " analagous results to 



* Journ de phys., Tom. xxxvii, p. 104. 

 f Mem. de VTmtitut pour I 'annexe 1808, p. 100, 103 and 

 107. 



