CHAPTER X. 



ALTITUDES. 



one would fashion a correct model of New Hampshire, he must 

 first ascertain the exact elevation of numerous points above the 

 ocean. As this has been our constant purpose from the very first, alti- 

 tudes have been collected by a study of canal and railroad surveys; 

 measurements have been made with mercurial and aneroid barometers ; 

 and numerous profiles have been obtained by careful levelling. A multi- 

 tude of observations have been collected, and it is the object of this 

 chapter to explain how they have been obtained, and to classify them 

 under various headings, such as may be convenient for future reference. 

 If any of our estimates are incorrect, the means of discovering the error 

 will here be afforded. 



The delineation of the geological sections across the state has been 

 based upon barometrical measurement, which could be obtained with little 

 additional trouble, at the same time with the examination of strata and 

 the collection of specimens of rocks. This method is, however, subject 

 to inaccuracies, owing to sudden fluctuations in barometrical pressure, 

 and other causes. The most reliable manner of obtaining extended series 

 of altitudes over a large area, so as to arrive with accuracy at the contour 

 or relative height and configuration of its whole extent, is to combine this 

 inexpensive barometrical work, carried in numerous sections across the 

 state, with transverse series of altitudes carefully obtained with an 



