1906.] NATURAL SCIENCES OF PHILADELPHIA. 573 



while others have completed their journey and now rest on the bowlders 

 at the edge of the ice. In 1906 an entirely new set of six plates was 

 prepared, and on July 12 they were laid out on the exact line used in 

 1899 (see map). Some defects having been found in the first plates the 

 ones laid out this year were of different design. A lighter steel reduced 

 the weight by one-half without decreasing efficiency, while the pipe 

 caulk was dispensed with entirely, a hold in the ice being obtained 

 by turning the right edge up one-half inch, and the left edge 

 down a like amount. The plate was thus held in position on the ice 

 should it turn over. It is made up of but one piece, and may be nested 

 compactly for carrying. Steel one-eighth inch thick was used, 6 

 inches by 7 inches, which was left 6 inches square after the edging up 

 had been completed. A trial showed that the thinner plate, allowing 

 greater melting of the ice beneath, formed a pocket in which the plate 

 rested, almost entirely free from slipping even on the steeper slopes. 

 Each plate was marked "VAUX, 1906" in white on a red lead back- 

 ground. The plates laid out were numbered from 1 to 6, beginning 

 on the right side of the glacier. 



The aim of this investigation was to compare the yearly rate of flow 

 at the line laid out with the yearly changes in the position of the 

 tongue, and to determine the effect which a change in one would have 

 on the other. As the second series of plates have been in position but 

 a short time no yearly comparisons can be made, but the following 

 table, comparing the daily motion of the plates in the fall of 1899 

 (compare Proc. Acad. Nat. Sci. Phila., 1899, p. 507) with the motion 

 of those in 1906, will give a ratio of the summer motion between the 

 two dates. The plates have been grouped according to their location 

 on the glacier, the numbers in the two instances bearing no relation to 

 each other. 



The great uncertainty of this work may be realized when it is noted 

 that in 1906 during twelve days the surface conditions of the glacier 

 changed completely. Crevasses opened, others closed, and plates 

 which when laid out were on comparatively level ice were found to be 

 in almost inaccessible positions, Avhich took long detours from the 

 main path to reach. 



The interval between the laying out and measuring of the plates 

 was one of unusual heat. Great freshets were reported all through the 

 district, every glacier stream was swollen to abnormal size, and evi- 

 dences of great surface melting were everj^here apparent. 



In addition to locating the position of the plates, a cross-section of 

 the surface of the glacier at this point was developed. A comparison 



