38 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



Table XX. — American storms advancing northerly and easterly. 



55. We see from this table tbafc stoim.s of tlii.s class occur most frequeutly in the autumn and 

 least frequently in the summer. One of these storms began near latitude 15°, two began near 

 latitude 20°, and seventeen of them began south of latitude 24°. Three of these storms had been 

 traveling towards the northwest, previous to the dates given in the table, and two of them came 

 from the northwest; but in the other cases the barometric depression was too small to allow us to 

 trace their course previous to the dates here given. For most of the cases in the last half of the 

 table this is clearly shown by the international observations, and we may therefore infer it to be 

 true in the other cases. As long as these storms continued south of latitude 30° the barometric 

 depression was generally small, but it increased as the storm advanced northward. In tifteen 

 cases the barometer fell below 29.5 inches, and in four ca.ses itl'ell below 29.0 inches. The average 

 velocity of progress of these storm centers, while a<1vancing northward and eastward, was 26.9 

 miles per hour. From a comparison of this table with Table HI we perceive that the American 

 storms which originate between the equator and latitude 20° N., generally travel towards a point 

 between north and west, but occasionally they advance almost exactly northward. 



56. In order to institute a compaiison between the peculiarities of these storms whicli travel 

 northward and those which travel almost exactly towards the south I have selected those storms 

 which passed near Galveston, Tex., and which pursued paths almost exactly opposite to those 

 shown in Table XVIII. Table XXI exhibits the leading phenomena of these storms, as deter- 

 mined by ^observations at five stations. 



