Summary and Conclusions 139 



conclusions is suggested by the method that was em- 

 ployed and the subject that was investigated. The 

 inquiry is a statistical study of an aspect of meteorology, 

 and, therefore, the caution to be exercised in the use 

 of the conclusions is the caution that should be applied 

 to statistical work in general and to meteorology in 

 particular. As far as the statistical work is concerned, 

 it should be observed that the data were drawn from a 

 limited area of the United States and covered, at most, 

 seventy- two years. Consequently, while there seem to 

 be very good reasons in favor of the belief that, for the 

 purpose for which they were used, the data were repre- 

 sentative of the whole country, it is highly desirable 

 that similar studies should be made for other places and 

 other times. Furthermore, the present investigation 

 was limited to a study of the periodicity of rainfall, but 

 a more adequate research would embrace the periodicity 

 of temperature and of other weather elements, together 

 with an investigation of the interrelation of the elements. 

 Before passing on to consider the caution to be observed 

 in the use of statistical studies of meteorology, a word 

 should be said in justification of the limitation of the 

 inquiry to the periodicity of annual rainfall. The ob- 

 ject of taking annual rainfall was to ascertain the mean 

 periodicity of the rainfall of the critical seasons of the 

 several crops. It would have been more satisfactory to 

 investigate the periodicity of the rainfall of the critical 

 season in case of each crop, but, because of the extreme 

 laboriousness of the calculations, a device had to be 

 adopted to limit the amount of computation. 



