524 THE POPULAR SCIENCE MONTHLY. 



overtake them in their descent ; and then the smaller stones will stick 

 to the larger and at once deform them. But besides the deformation 

 caused by the presence of the smaller stone, the effect of the impact 

 may be to impart a rotary motion to the stone, so that now it will no 

 longer continue to grow in the same manner as before. Hence we 

 have causes for almost any irregularities of form in the ordinary hail- 

 stone. 



Fig. S. Imitation in Plaster of Paris. 







It appears, from the numerous accounts which have been pub- 

 lished, that occasionally hailstones are found whose form is altogether 

 different from that described above. These, however, are exceptional, 

 and, to whatever causes they may owe their peculiarities, these causes 

 cannot affect the stones to which reference is here made. 



Again, on careful examination, it is seen that the ordinary hail- 

 stones are denser and firmer toward their bases or spherical sides than 

 near the vertex of the cone, which latter often appears to have broken 

 off in the descent. This, also, is exactly what would result from the 

 manner of formation described above. When the particle first starts 

 it will be moving slowly, and the force with which the particles im- 

 pinge upon it will be slight, and consequently its texture loose ; as, 

 however, it grows in size and its velocity increases, it will strike the 

 particles it overtakes with greater force and so drive them into a 

 more compact mass. If the velocity were sufficient, the particles 

 would strike with sufficient force to adhere as solid ice, and this ap- 

 pears to be the case when the stones become large, as large as a wal- 

 nut, for instance. 



An idea of the effect of the suspended particles, on being overtaken 



