CLIMATOLOGY, 



CLIMATOLOGY, NO. 3. 



BY A CONSTANT READER. 



The summer climate of the United States is remarkable in many respects. The mean 

 temperature of its southern portion exceeds that of the tropical region to the south of it. 

 The Isotheral line, or Isothere (that is, the line of equal summer temperature) of 80°, 

 follows the coast of the Gulf of Mexico and the Atlantic, from the southern point of Texas 

 to that of North Carolina. It then, in latitude 340, sweeps round to the W. and S. \V., 

 bending very gradually to the N., till, in the N. E. part of Texas, it again approaches lati- 

 tude 34^. It is then bent to the S. by the high table-lands of Texas, crosses the Pecos in 

 latitude 29^, and sweeps to the N. W., till, in the neighborhood of Lake Humboldt, it reaches 

 the' parallel of 40°; and is then bent suddenly round by the Sierra Nevada Mountains, 

 and sweeps S. S. E. along the eastern coast of the Califomian Peninsula. 



The space within the Isothere thus described, includes one of the hottest regions of the 

 globe. Its focus is the district from the head of the Gulf of California to the mouth of the 

 Gila, where the mean summer heat is 90O, while that of the West India Islands is 81^. 

 West of the Sierra Nevada, along the valley of the San Joaqiiim, is another district of intense 

 summer heat, the mean of the thermometer at Fort Miller in that valley being 850. This 

 belt of intensely heated country follows the southern line of the coast along the Gulf, and 

 is limited in the interior by the Mexican table-lands, which extend to lat. 30°, and of which 

 the height is six or eight thousand feet, and the mean summer heat is 680. Within this hot 

 belt the mean heat ranges from S20 to 85°. The influences of this intense heat are modified 

 by the moisture or dryness of the climate. 



In the southern part of the Peninsula of Florida, twenty-five inches of rain fall in the 

 three summer months ; twenty-two inches fall in the rest of the peninsula ; twenty inches 

 in the remaining region east of the Mississippi. Through Eastern Texas the summer rains 

 average twelve inches, gradually lessening to ten and eight inches at the W. and S. W. 

 Three inches fall along the valley of the Rio Grande ; one and a half inches on the Gila, 

 and the prolonged point of the belt to the N. W., traverses the rainless desert of Utah. 



We have, then, in our southern borders, an extensive range of summer tropical climate, 

 capable, in its eastern portion, of maturing all the annual fruits and plants of the hottest 

 regions of the globe ; and, wherever it can be irrigated in its western portion, susceptible of 

 the highest fertility ; for the Basaltic rocks of that region disintegrate into one of the most 

 genial of soils, which will, at some future day, when science shall direct the industry of its 

 people, rival the ancient fertility of the now desert valleys of Persia and Syria, and " blossom 

 like the rose." It is highly favorable to the future prospects of these sterile regions, that 

 the summer rains on the mountains are copious and frequent ; so that, by damming uj) the 

 ravines and mountain valleys, artificial lakes may be formed for the irrigation of the subja- 

 cent districts. 



Tlic adaptation of this hot belt to the cultivation of tropical trees, is controlled by its 

 winter climate. The Isocheimal line, or Isocheim (the line of mean winter temperature) of 

 650, passes through the peninsula in latitude 27^, say 120 miles from the cape. South of 

 that line, it is probable that neither ice nor frost is ever known, and that the Clove-tree, 

 the Pimcnta, the Date Palm, the Coffee-tree, and the Cacao, would thrive luxuriantly. The 

 Isocheim of 60° passes across the peninsula at St. Augustine, and enters Texas in latitude 

 270. South of that line, the olive, the fig, the orange, and the lemon, would flourish. 



The Isocheim of 55° crosses the mouth of the St. Johns, and passes along the northern 

 of the Gulf to Matagorda, thence W. and W. N. W. to the mouth of the Gila. South 

 line, winter frosts occasionally occur, and cut oQ" the orange-trees of Northern F' 



