166 Walker's Statistical Atlas of the United States. 
The estimated average annual rain-fall is given for each of 
the basins of the map. If now we continue our comparisons 
the former and 43 for the latter. The first is probably too 
high. Plate V. isa ‘Rain Chart of the United States,” pre- 
pared, by Chas. A, Schott of the U. S. Coast er under “ 
of water falling in each entire basin, we find them very nearly 
equal,—that in the Missouri basin to that in the Ohio basin as 
about 1-1 to 1. Considering the vastly greater area for evapo- 
ration in the former, 2°65 to 1, and the dryer atmosphere, we are 
rather celine that the = excess of water dis- 
charged by the Ohio is not greater than it is. According to 
the report dees the mean dacaice of the Missouri River is 
120,000 cubic feet per second, of the Ohio 158,000. On the 
rain-chart, much or most of the basin lies inside of the line of 
12 inches annual rain- -fall, and only op very smal] part that 
lies below Atchison, Kansas, has 82 or more inches. On the 
same chart the lowest rain-fall of the Obi Valley is 36 inches, 
reaching 62 in its extreme southern part 
Plate VIL, “ Temperature Chart of the United States” (of the 
same authority as Plate V.) shows that the mean annual tem- 
perature of the Missouri basin is about 10° F. less than that of 
the Ohio. The isothermal line of 48° F. at lon. 110° W. is in 
lat. 48°. It sweeps down near or a little above the center of 
the Missouri basin, crossing the river at Fort Randall, sinking 
to lat. 39° in southern Iowa (more than 600 miles south of our 
starting point), then it rises again eastward so as to keep en- 
tirely outside of the Ohio basin. Very ei all the Ohio 
basin lies between the isothermals of 50° and 60°. The Mis- 
souri basin has a much wider range. 
ven more suggestive is a comparison of these two basins 
with ages ies which is an “U.S. Signal Service Chart” 
showing th an temperature at 4.35 P. M. of each day “of 
the hottest ut of 1872” (by pe Tines), and of the 7.35 A. M. 
observations “of the coldest week” of the winter following (by 
blue lines). It will be seen that this chart does not t show the 
act 
rvat 
a a comparison of the coldest “ spell” of the van with the hot- 
this, we find the greatest difference near the eastern 
hat of the Rocky Mountains, or on the plains eastward. At 
Fort Benton this difference is upward of 102° Fahr. It di- 
