162 PROF. O. REYNOLDS ON THE FORMATION OF 



The Shape and Structure of ordinary Hailstones. 



On close observation I had founds what had previously 

 been noticed by other observers, that the shape of an or- 

 dinary hailstone is not what it at first sight appears to be. 

 They are not spheres more or less imperfect, but more or 

 less imperfect cones or pyramids with rounded bases, like 

 the sectors of spheres — the conical surface being striated, 

 the striae radiating from the vertex of the cone. 



In texture the hailstones have the appearance of being 

 an aggregation of minute particles of ice fitting closely 

 together, but without any crystallization such as that seen 

 in the snowflake ; while, on careful observation, it is seen 

 that they are denser and firmer towards their bases or 

 spherical sides than near the vertex of the cone, which 

 latter often appears to have been broken off" in their 

 descent. 



As I explained, it seemed to me that this form and 

 structure was exactly such as would result from the manner 

 of aggregation which I had supposed. When a particle 

 which ultimately forms the vertex of the cone starts on its 

 downward career and encounters other particles, these 

 adhere to its lower face. The mass, therefore, grows in 

 thickness downwards ; and as some of the particles strike 

 the face so close to the edge that they overhang, the lower 

 face continually grows broader, and a conical form is given 

 to the mass above. 



When a particle first starts, it moves slowly, and the 

 force with which it meets the other particles is slight, and 

 consequently its texture is loose ; but as it increases in size 

 and velocity, it strikes the particles which it overtakes 

 with greater force, and so drives them into a more compact 

 mass. 



Assuming that the temperature at which hailstones are 



