The vectors of sag in mm are plotted along the Y-axis and the time in seconds along the 

 X-axis. The figure shows clearly the peculiarity of all flexures during motion, namely: the front 

 incline of the curve of sag is steeper than the rear. I explain this phenomenon by the fact that 

 during tlie movement of a load, inertial forces act in a direction opposite to the direction of the 

 movement. As a result of this, ice flexure is retarded in front of the load and the straightening 

 out of the ice is retarded behind the load. 



As a result, while the load is moving, the curve of sag ceases to be symmetrical. Its front 

 incline is steeper than the rear, and this difference is greater, the greater the velocity of the 

 movements. 



Figure 65. Oscillation of the ice on Kuznechikha 

 River to January, 1942. 



Figure 65 shows the ice sag during the 2 January, 1942 crossing of an electric train and a 

 loaded car (total weight, 74 tons) across the same crossing. The following was recorded by a level 

 at the time of this crossing: at first the leveling rod set up on the tracks, dropped 3 mm, then rose 

 28 mm, and at the instant the unit crossed it fell to 128 mm, and then after several small oscilla- 

 tions the rod proved to be 8 mm lower than the initial position (residual deformation). The smallest 

 thickness of ice at the time of this crossing was 46 cm. The speed of the crossing was 15-20 

 km/hour. 



We will notice the basic difference when we compare figures 64 and 65. The graph obtained 

 on 29 January 1942 at a low speed of movement (about 3 km/hour) shows no oscillations in the ice; 

 with a high speed of movement, the wave-like deflections of ice can easily be seen on the graph 

 2 January 1942. This phenomenon is explained by the fact that the ice deflection is transmitted by 

 the water and the waves in the ice are a result of the waves which had formed in the water under 

 the ice. 



I consider that the wave-like deflections of the ice noted on 2 January, 1942 on the 

 Kuznechikha River are ex-plained, namely by this fact. The load, when moving from the shore to 

 the ice, bends it so that a singular angled basin develops in the ice under the weight of the load. 

 This basin, with its angular sides, is moving in space and compressing the water in its path, 

 creates waves in the latter which in their turn, moving in space according to general laws, force 

 the ice to bend in conformity with their shape. 



195 



