52 A. ]V. (irirclij — (rrographjj of ilic Air. 



most cases. These fall lines are intersections oi i)lanes Avith a 

 cone whieli graphically represents the totality of temperature- 

 fall, the contents of the cone being equal to the area of its base 

 multiplied by its altitude, which is the greatest fall in tempera- 

 ture at the center of the cold wave. 



A formula has been devised, based on 127 special cases, repre- 

 senting the amount of fall in terms of the amount of barometic 

 depression in a " low," and the amount of excess if a " high," and 

 the density of the isothermal lines in the region. 



From proper consideration of the type of low area, shape of 

 isobars, and position of the long axis, definite conclusions can 

 be drawn as to the subsequent shape of the elliptical twenty- 

 degree temperature-fall area and its position. 



A method has been devised, also by Professor Russell, for de- 

 termining the maximum fall of temperature at the center of the 

 cold wave. The maximum fall and extent of fall being known, 

 from suitably })repared tables, the area of twenty-degree fall can 

 be derived. Previously prepared pieces of card-board are laid 

 in the proper position on a map of suitable scale, and lines 

 drawn around them. Between the line representing the twenty- 

 degree fall and the center, the other falls of thirty degrees, forty 

 degrees, etc., are sketched in. 



The foregoing sketch of the geography of the air may a^jpear 

 too superficial and limited for the purposes of this Society, but 

 its further elaboration was im|)racticable. Indeed, the subject 

 of meteorology could hardly have been touched upon this year 

 had it not been for the courtesy of Professor Russell in placing 

 at my disposal notes upon translations from foreign publications, 

 especially from the German ; which publications I have been 

 unable to examine save in a casual Avay. 



The address, as it is, is submitted only in the hope that it may 

 serve, if no other purpose, at least to indicate the great interest 

 which now obtains in the geograph}'^ of the air, and Avhich mani- 

 fests itself in the production of metecn-ological pamphlets and 

 publications too numerous to permit any one charged Avith im- 

 portant executive duties to examine them all, even in a non- 

 critical way. 



