70 Dr Forry on the Climate of the United States. 



These data were allowed to accumulate in the Medical 

 Bureau for twenty years, before any comprehensive attempt 

 was made to determine their relations to one another, and to 

 deduce from them general laws ; and it fell to our lot, under 

 the direction of the present Surgeon-General, Thomas Law- 

 son, Esq., to present a systematic arrangement of these iso- 

 lated facts, embracing the climatology of a vast district, 

 extending from the oldest settlements on the Atlantic shores 

 to the farthest outposts of civilized occupation, even to the 

 coasts of the Pacific. Thus were presented, under the sanc- 

 tion of the War Department, unlike all other treatises on 

 the same subject, which are generally loosely written and 

 made up of the most vague and general statements, deduc- 

 tions based upon precise instrumental observations. 



As regards the phenomena of superficial terrestrial tem- 

 perature, let it here suffice to refer to its dependence upon 

 two classes "of causes, viz. those resulting from celestial 

 relation, and those produced by geographical position. The 

 former, which may be called the primary constituents of 

 climate, result from the globular figure of the earth, its di- 

 urnal motion upon its axis, and the obliquity of its motion in 

 an elliptical orbit in regard to the plane of the equator. 

 Now, if this class of causes solely controlled the phenomena 

 of teiTesti'ial temperature, climates might be classified with 

 mathematical precision ; but the efi'ects produced by solar 

 heat are so much modified by local causes, that the climatic 

 features of any region can be determined only by observa- 

 tion. It is these last, the secondary constituents of climate, 

 that we have chiefly to do with in the present inquiry ; and 

 among these geographical or local causes, the following may 

 be regarded as the principal : — 1. The action of the sun upon 

 the surface of the earth. 2. The vicinity of great seas and 

 their relative position. 3. The elevation of the place above 



portableness ; but, liOTvever well it maybe adapted to tlie humid climate 

 of England, experience soon demonstrated its inapplicability to the arid 

 atmosphere of the United States, with the exception, perhaps^, of our 

 southern borders ; and hence has been imposed upon the Department 

 the necessity of using the wet bulb thermometer iu determining the 

 hygrometric conditiou of the air. 



