XX EXPLANATION OF THE PLATES. 



Plate XIII. — The data for this Plate arc furnished by Maury's Storm and 

 Itain Charts, including observations for 107,277 days in the North Atlantic, and 

 158,025 in the South; collated by Lieutenant J. J. Guthrie, at the Washington 

 Observatory, in 1855. 



The heavy vertical lines, 5°, 10°, 15°, etc., represent parallels of latitude; the 

 other vertical lines, months ; and the horizontal lines, per cents., or the number 

 of days in a hundred. 



The continuous curve line stands for phenomena in the North, and the broken 

 curve line for phenomena in the South Atlantic. Thus the Gales' Curve shows 

 that in every hundred days, and on the average, in the month of January of 

 different years, there have been observed, in the northern hemisphere, 36 gales 

 (3G per cent.) between the parallels of 50° and 55° ; whereas during the same 

 time and between the same parallels in the southern hemisphere, only 10 gales on 

 the average (10 per cent.) have been reported. 



The fact is here developed that the atmosphere is in a more unstable condi- 

 tion in the Tsorth than in the South Atlantic ; that we have more calms, more 

 rains, more fogs, more gales, and more thunder in the northern than in the 

 southern hemisphere, particularly between the equator and the 55th parallel. 

 Beyond that, the influence of Cape Horn becomes manifest. 



ife Plate XIV. (§ 839) shows the limits of the unexplored area about the south 

 pole. 



Plate XV. shows by curves the prevalence of winds with northing as compared 

 with winds with southing in them in each of the two hemispheres, north and 

 south. 



Plate XVI. shows the Barometric Curve projected according to actual obser- 

 vations at sea, from the parallel of 78° north to the parallel of 56° south, and 

 carried thence to the poles, by conjecture and in conformity with indications. 



