Dr. A. Waller's Microscopic Observations on Hail. 109 



escaping. At the time I commenced these observations I was 

 not aware that this structure of the hailstone had ever been 

 ascertained before, but I now find that it has been already 

 stated by several authors. Descartes, who admitted the ex- 

 istence of clouds composed of solid globules, explained the 

 formation of hailstones by some of these globules being de- 

 tached, and I believe agglomerated together. Berzelius, who 

 gives in his Treatise on Chemistry a succinct and excellent 

 account of hail, attributes it to the " agglomeration de plu- 

 sieurs grains," " arrondis et non en cristaux comme la neige." 

 In the Encyclopaedia Britannica, art. Hail, we find also that 

 hail is formed " by many little spherules of ice agglutinated 

 together." It appears surprising, that with such correct de- 

 scriptions of hail there should still exist in works of a more 

 ambitious character, others so much more imperfect ami 

 erroneous. In fig. 1. I have traced the forms of these glo- 

 bules : some of them appear more ovular than globular, and 

 I believe that such is the real shape of some ; although at 

 the same time we must bear in mind, that a transparent glo- 

 bule of the high refractive powers of water will appear much 

 distorted if part is seen through others before it, while the 

 rest of it is perfectly exposed. The average size of those I 

 have represented is about one-third of a millimetre; they do 

 not vary greatly from this standard, and I have found them 

 generally the same on other occasions. 



It is evident that these globules must have existed in a solid 

 state previous to their agglomeration to form hail, and there- 

 fore their maximum temperature at that time must have been 

 below the freezing-point. 



In what manner are we to account for the formation of 

 these globules previous to their agglomeration? 



In the experiments on congelation under the microscope, the 

 account of which has been given in the paper before referred 

 to, we have already seen with what facility these globular forms 

 of ice are produced by the condensation of the moisture from 

 the atmosphere on a surface of glass or Canada balsam. A 

 curious and unforeseen analogy was found between their ap- 

 pearance in my experiments and their formation in nature. 

 In winter a refrigerating mixture causes a deposit from the 

 air, in which crystalline forms, frequently of a very regular ap- 

 pearance, were generally perceived. Only at a few points were 

 discovered globular forms of ice, and these were generally 

 surrounded on their surface with minute pyramidal crystals, 

 giving them a mace-like appearance. 



In summer the deposit was more confusedly crystalline, 

 liable to liquefy from various external causes, and then to re- 



