LETTER TO CAPTAIN HUMPHREYS, TOPOGRAPHICAL ENGINEERS. 
Smrrusonran InstiruTion, Washington, March 1, 1856. 
Sm: During the first organization of the parties for the survey of a railroad route to the 
Pacific, application was made to the Smithsonian Institution, by the officers in charge, for in- 
structions and suggestions in reference to the investigation of the Natural History of their 
respective lines. These were cheerfully furnished, as in accordance with the objects of an 
establishment intended for the increase and diffusion of knowledge. The specimens in Zoology, 
as collected, were transmitted from time to time to the Institution, and properly preserved 
until the return of the parties. A series of special reports was prepared by the naturalists of 
the expeditions; but as these were necessarily disconnected and incomplete, it was deemed 
advisable to furnish a general systematic report upon the collections as a whole ; and this being 
sanctioned by the War Department, the materials were entrusted to competent individuals for 
this purpose, the necessary drawings being made by a skilful artist within the walls of the 
Institution. 
The first part of the general report having been already furnished, I now transmit the 
remainder, with the hope that its execution will be satisfactory to the Department. 
Very respectfully, your obedient servant, 
JOSEPH HENRY, 
Secretary Smithsonian Institution. 
Captain A. A. Humpureys, Zopographical Engineers, 
In charge of Office of Explorations and Surveys, War Department. 
