246 PROCEEDINGS OF THE OHIO ACADEMY OF SCIENCE. 



long enough so that accidental coincidences will be eliminated, 

 then to develop a practical method of comparing the yield with 

 definite weather conditions for definite periods of time. 



The United States Department of Agriculture and the dif- 

 ferent State Boards of Agriculture have been collecting crop 

 yield statistics for a good many years. In Ohio the yield figures 

 for the staple crops are available for the different counties for 

 each year since 1850. At the same time the United States 

 Weather Bureau has been keeping daily records of the various 

 weather factors for over 40 years at its regular stations and has 

 been collecting similar data as regards rainfall and temperature 

 at thousands of cooperative stations well distributed over the 

 country. 



There have been enough of these voluntary and regular 

 stations in Ohio to give a reliable State average for the tem- 

 perature for each month from 1850 to date and for the rainfall 

 since 1854. Although not many States have a record to equal 

 this they nearly all have these data for a considerable period 

 of time. 



We have used three dififerent methods for determining 

 whether there is a relation between certain weather factors and 

 the yield of crops. These are the plotted curve, the dot chart, and 

 the mathematical calculati"on for giving the measure of relation 

 between two factors as expressed in the correlation coefficient. 

 The first two are graphical while the third is the method de- 

 veloped by Bravais, Galton, Edgeworth, Pearson, and Yule. 



WEATHER AND THE YIELD OF CORN 



Inasmuch as 75% of the world's production of corn is grown 

 in the United States, and as this is easily the most important 

 crop in Ohio, this crop was used in our first complete study. 

 These studies have determined that the most important weather 

 factor in varying the yield of corn is rainfall and the most im- 

 portant period, considering calendar months is July. 



The average rainfall for Ohio in July is almost exactly four 

 inches while the average yield of corn for the State for the past 



