SMITHSONIAN MISCELLANEOUS COLLECTIONS. 



— 236 



CmCULAIl P.ELATIYE TO HEIGHTS. 



For the purpose of forming a general map of the North 

 American Continent, exhibiting the plains, mountains, valleys, 

 etc., the Smithsonian Institution has collected a large amount 

 of material relative to altitudes, which has been placed in the 

 hands of W. L. Nicholson, Esq., Topographer of the U. S. 

 Post-Office Department, to be discussed and elaborated. 



There must, however, still remain in the hands of indivi- 

 duals and corporations, records of an important character, 

 which would be of great value in properly carrying out the 

 enterprise. It is, therefore, respectfully requested that printed 

 copies, or original manuscripts of records, especially of j^lot- 

 ted profiles or maps pertaining to this subject, be forwarded 

 to the Smithsonian Institution. 



In stating the heights, as furnished by surveys for raih'oads, 

 whether actually constructed, or only projected, it is desirable 

 that the levellings be referred to some known point on con- 

 necting or intersecting roads, or to the water-surface (high- 

 water, low-water, or mean-tide) of the ocean, or of one of the 

 great lakes, or to the level of a noted stage of water (high or 

 low) of some rivex*. The crossings of the watercourses, ridges, 

 and summits are particularly desired, as well as all conside- 

 rable and characteristic changes of level, giving, where much 

 difference exists, both grade-line and original surface; the 

 levels of all intersections with other roads are impoi'tant as 

 means of comparison, and for checking results. 



Due credit will be given to all contributors to this work. 



JOSEPH HENRY, 



Secretary Smithsonian Institution. 



Smithsonian Institution, "Washington, D. C. 



