Vol. 5I .] 



PLOW OF A VISCOUS FLUID. 



365 



Layer. 



I. 



Original 

 Height. 



II. 



Amount of 

 Depression. 



Ratio of I. to II. 



1 



13-5 



21 



41 



54 



4 



8-5 

 22 

 33 



10:3 

 10:4 

 10 : 5-37 



10 : 6-1 



2 



3 



4 (original surface) ... 



The downward movement of the original surface of the ' glacier ' 

 at this section is thus seen to amount to almost four-fifths of the 

 superficial movement down the slope, for the latter, as previously- 

 stated, was at this place 0*5 mm. per diem, or 43-5 mm. for the 

 total of eighty-seven days that the experiment lasted. The under- 

 lying layers have evidently been less affected the greater their 

 proximity to the bottom, but none have escaped disturbance 

 altogether. 



The total upward movement near the opposing edge of the barrier 

 can only be determined in the 



case of the two lower layers, 

 since the others were involved 

 in the rapid flow due to the 

 plunge of the material over the 

 barrier. The dotted line r r r 2 r 3 

 in fig. 3 shows the direction along 

 which the particles lying along 

 it have travelled ; in the case of 

 layer no. 2 the movement along 

 this line has carried a globule 

 of sago, which was originally 

 situated at r 2 , upwards and 

 forwards to r 3 , a distance of 20 

 to 21 mm. ; the vertical dis- 

 placement is 16 mm., the hori- 

 zontal 14 mm. Layer no. 1 

 has been similarly affected ; 

 the displacement from r to r 2 

 amounts to 20 mm. ; the hori- 

 zontal and vertical components 

 are nearly equal, and measure 

 about 10 mm. each. It is 



Fig. 4. — The back of the ' glacier ' 

 at the conclusion of the expe- 

 riment. 



Layers 1, 2, 3 are seen not to have 

 suffered any displacement here, owing 

 to the adhesion of the pitch to the back 

 of the trough. Above 3 the pitch is 

 fractured, so as to expose an obliquely 

 transverse section of the original sur- 

 face (4) and the succeeding layers. 

 Subsidence is at a maximum near 

 the middle, adhesion having prevented 

 much movement near the sides, 

 interesting to compare these 



deep-seated movements with those of the surface over the same 

 region, which is comprised between the lines 90 and 115 mm. from 

 the origin ; we have already seen that at 90 mm. the surface-flow 

 was 1-5 mm., and at 115 mm. it was 2 mm. per diem, so that in 



