"While climatological observations have been steadily accumulating for the last quarter of a century, the general results are inaccessible, not only to the general public but also to tho great majority of students and investigators interested in the advancement of scientific agriculture in the United States. The work herewith aims to present in form for ready reference comparative climatic statistics for the different portions of the United States, accompanied by explanatory charts and text. The charts and text figures are necessary to a proper understanding of the text"--Letter of transmittal.