PROCEEDINGS OF THE OHIO ACADEMY OF SCIENCE. 



249 



$250,000,000 it must be true that rainfall in July is the dominat- 

 ing weather factor in the production of corn, in the United States. 

 In figure 2 the importance of rainfall in July is emphasized 

 and it is made clear that the variations in mean temperature in 

 July do not greatly afifect the yields of corn. This is the second 

 graphical method employed and is called the "dot chart." This 



Figure 2. Dot chart showing the combined effect of temperature 

 and rainfall during the month of July upon the yield of corn in Ohio, 

 1854 to 1913. 



chart is a most practical method for showing the effect of two 

 factors upon a third. 



In this case the combined efifect of temperature and rainfall 

 during the month of July upon the yield of corn is indicated. 

 That temperature does not have a material efifect is made 

 plain by the fact that there were just as many good yields of 

 corn when the temperature was above the normal as when it was 

 below the normal. On the other hand the plus marks, showing 



