GENERALIZATION OF THE PRECEDING TABULAR RESULTS 



CONSTRUCTION OF RAIN-FALL CHARTS OF THE UNITED STATES. 



The mutual relations and significancy of the tabular results can best be brought 

 out by a graphical representation. In this form the amount and general disti'ibu- 

 tion of the rain-fall over the country can at once be seen, and admit, at the same 

 time, a close study of its special features. The increased material at disposal since 

 the publication of the first edition of these tables, and the importance to the agricul- 

 turist of a knowledge of the distribution of the rain-fall in the several seasons, induced 

 the Institution to enlarge the charts as well as to construct two new ones, thus present- 

 ing five, viz., one for the year and one for each of the four seasons. 



CONSTRUCTION OF THE RAIN-FALL CHARTS. 



For the delineation of the geographical disti-ibution of the aqueous precipitation 

 over the area of the United States the same base-map has been made use of which 

 served for the exhibition of the distribution of the atmospheric temperature, pub- 

 lished by the Smithsonian Institution in 1876. =•■' It has, however, been improved by 

 the introduction of the mountain systems, and it is believed that the study of the 

 relationship of the distribution of temperature and of rain-fall will be facilitated by 

 this uniformity of projection and scale. For the generalization of the results of the 

 greater part of the western and elevated portion of the United States, the scale of 

 the map appears inconveniently large, our material being too limited to adequately 

 cover so large an area, otherwise it is well adapted for the exhibition of the general 

 and the detciil features presented in the numerical results. To explain the construction 

 of these charts it suffices to show it for the one exhibiting the annual distribution. 

 All stations for which the observations extended over four or more years were plotted 

 by their coordinates, latitude and longitude, and against the dot was written the 

 amount of precipitation in inches and to the nearest tenth of an inch ; for all other 



« Smithsonian Contributions to Knowledge, No. 277, " Tables, Distribution, and Variations of tlie Atmospheric Temperature 

 in the United States." By Charles A. Schott. Washington, 1876. 



(187) 



