Davis— Rubbed String. 



The short side of each integral surface is to be taken as the 



axis, the long side as the t axis. All contours below sea-level 



■e drawn with dashes. In some cases, parts of the contours 



e dotted in to show more clearly the nature of the sur- 



It would not have been easy to draw the surfaces on 



scales which corresponded to a single bowing speed, or in any 



other comparable fashion. The number of contours in each 



surface is, therefore, arbitrary, and their density in different 



surfaces indicates only roughly the relative slopes or heights of 



those surfaces under similar conditions. For exact information 



of this kind the reader is referred to Figures 1, 9, and 11. 



Proc. Amer. Acap. arts and Sciences. Vol. XLI. 



