166 Dr. Waller's additional Observations on Hail, 



tides, which, from their size, form and colour, nearly resem- 

 bled the eggs of the common blow-fly. At about 2 p.m. the 

 snow fell more thickly, under the form of small conglomera- 

 tions or balls, varying from the size of lialf a pea to three or 

 four times larger. Pressed between the fingers, some of these 

 pellets of snow were easily crushed ; only a few offered any 

 degree of resistance. To the naked eye they appeared to 

 consist of spongy crystalline particles: under the microscope 

 they were found to be composed of small regular crystals 

 nearly cubical, mixed with others more irregular of complex 

 outlines : the regular forms were exactly similar to the crystals 

 of frost and the cube-like particles found in the snow on the 

 day preceding. One of these balls submitted to the micro- 

 scope on a slip of glass, began slowly to liquefy, from the con- 

 tact of the glass and of the surrounding air. As this was 

 taking place the liquid was diffused by capillarity over the en- 

 tire mass, without any trace of moisture appearing externally 

 until the entire ball was in a state of semi-fusion, and of a dull 

 and semi-transparent white like a small hailstone: at the same 

 time the ball contracted in size and assumed a biconvex or 

 lenticular shape. While these changes were taking place the 

 crystals became fused at the angles and edges, most of them 

 becoming globular and ovular: in this condition several of the 

 balls were exposed to the open air, then several degrees be- 

 low the freezing-point. When examined the next morning 

 they were found perfectly hard, of a regular lenticular shape, 

 of a dull white colour, in every respect like certain hailstones 

 which I had collected during the summer. Under the mi- 

 croscope elliptic and circular particles were seen, like those 

 composing hailstones. Previous to and during their fusion, 

 bubbles of air were seen exactly as in the hailstones, though 

 in less abundance. Some of these were enclosed, as repre- 

 sented at p. 105, vol. xxviii. Phil. Mag. This observation 

 shows in a direct manner, with a much greater degree of 

 precision than I could have anticipated, the process of for- 

 mation of hail as it takes place in general. In the first place, 

 an agglomeration of crystalline particles, probably in conse- 

 quence of certain vorticose currents, takes place in a globular 

 shape. The ball of snow, thus formed by the capillary attrac- 

 tion which it possesses from its porous structure, absorbs any 

 moisture that may exist around it. The effect of this moisture 

 is twofold; first, as modilying the angular outlines of the com- 

 ponent particles ; and secondly, as binding them together into 

 a consistent mass, which any further abstraction of caloric 

 will reduce to the state of a hard and solid hailstone. If the 

 addition of moisture is considerable, the liquefaction of the 

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