93 [ 237 ] 



PART II. 



I. Determination of altitude by the barometer. — The ordinary methods 

 of ieveUing are slow, laborious, and sometimes almost impracticable, in 

 inoiintainous countries. Hence it is, doubtless, that we have so long neg- 

 lected to collect fiicts relative to the elevation of different regions of the 

 earth's surfl\ce above some fixed level, such as that of the ocean. But, 

 now that science has placed within the reach of everybody the admirable 

 instrument known as the barometer, has rendered it so applicable to the 

 irjcasurement of heights, and has so perfected it as to be capable of results 

 whose precision can be all that is desired, observations by it are being mul- 

 tiplied everywhere; j)ersons learned in sciences and arts are becoming con- 

 tributors : and we have reason to hope very soon for great advancement in 

 the knowledge of the relief of the surface of the earth — a knowledge in- 

 dispensable for civil and military purposes, for physical geography, for geol- 

 ogy, and for topography. 



impressed with the importance of this subject, I should have been want- 

 ing to the plan I had proposed for myself, if, from the very commencement 

 of my travels in the United States, 1 had not endeavored to add my contri- 

 bution to researches in this regard, and in respect to which the country 

 seemed to me almost (so to speak) untrodden. I was provided with sev- 

 eral barometers and accessories; and I found them also, very commonly, 

 in public institutions. I was yet in want of voluntary assistants. I found 

 them always, readily, among the enlightened men who are spread in 

 universities, in colleges, and in society; and from the year 1S33, I was 

 even able to institute a system of meteorological observations, taken four 

 or five times a day, at different places, simultaneously with my own ; which 

 daily extended itself as I advanced farther and farther into the country 

 I wished to visit, until it came to embrace a large surface of the territory 

 of the United States ; thus always affording me, in whatever part of the 

 field of my operations 1 might be, some station with which I could com- 

 pare my observations. Under this system has grown a considerable mass 

 of observations ; more than two-thirds of which yet remains to be calcu- 

 lated, and to appear hereafter, independently of such as I publish now, on 

 the occasion of the map. 



And here I cannot deny myself the pleasure of making public ac- 

 knowledgments to the several persons who, in this particular, have given 

 me their time, and honored me with tbeir assistance ; nor can I avoid 

 the duty which obliges me, as 1 think, (and which I hope their delicacy 

 will not be pained by my discharging,) to indicate them by name. Cer- 

 tainly, he who, in the measure of his opportunities and position, supports 

 and furthers science, when it is being directly contributed to by the en- 

 tire devotion and labor of another, merits, almost as much as that other, 

 the gratitude of the public. Assured that every reader will partake of 

 my sentiments on this subject. I shall, witliout further prelude or apology, 

 acknowledge the services 1 have received, in this respect, from the Rev. 

 A. Verot, professor of mathematics and natural philosophy at St. Mary's 

 OoUege, Baltimore ; the Rev. J. Wallace, professor in the university, Co- 

 lumbia, S, C; my friend. Professor H. Guenebault, lately of Savannah, Ga., 



