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Questions for Solution relating to Meteorology^ Hydrography^ 

 and the Art of Navigatioru By M. Abago. (Continued 

 from Vol. XX. p. 405.) 



Mean height of the Barometer. — A few years ago a positive 

 denial would have been given to the assertion, that there is any 

 permanent difference between the barometrical heights corres- 

 ponding in the different regions of the globe to the level of the 

 sea. At present such differences are regarded as not only pos- 

 sible but even probable. The officers of the Bonite ought there- 

 fore to prieserve their barometer with the most scrupulous care, 

 in a fit state to make observations by which every variation may 

 be registered for the purpose of comparison. Notice should 

 never fail to be made of the exact height of the bulb of the ba- 

 rometer above the level of the sea. 



Of the influence of different "winds on the heights of the Ba- 

 rometer. — As soon after the memorable discovery of Toricelli 

 as meteorologists directed their attention to the observation of the 

 barometer, they perceived that in general certain winds pro- 

 duced a rapid ascent of the mercurial column, while opposite 

 winds produced a contrary effect in a manner equally decided. 

 The difficulty was to determine the numerical value of these in- 

 fluences. It was necessary, in order to evade entirely passing 

 and fortuitous influence, and obtain the true measure of perma- 

 nent causes, to operate in great numbers ; to form an estimate 

 from a long series of good observations made in the same locality ; 

 to group the winds by their precise directions ; and to deduct 

 the means of effects purely thermometrical. 



Burckhardt undertook this labour, availing himself of twenty- 

 seven years of observations which Messier had made at Paris 

 from 1773 to 1801. If we designate by the letter H. the mean 

 height of the barometer at Paris, that is to say, the height deter- 

 mined by the average of all the observations, the means corres- 

 ponding to the different winds, according to Burckhardt*s calcu- 

 lations, will be as follows : — 



