1 64- Dr. Waller's additional Observations OJi Hail, 



posed with equal regularity. We may distinguish them readily, 

 inasmuch as the globules of water soon disappear, whereas these 

 beads are permanent, and unaffected by the vacuum of the 

 air-pump. Mr. Blackwall has described them fully in the 

 Transactions of the Linnaean Society. 



Numerous particles of an organic nature may be detected 

 in rain. But this investigation is liable to many errors 

 which do not exist with regard to hail ; because a solid body 

 of ice will remain completely free from all foreign particles in 

 the lower strata, and only contains those which were fixed 

 within it at the moment of its solidification; while in rain we 

 find a mixture of foreign bodies derived from various sources, 

 which the drop of water meets on its passage from the point 

 at which it is formed to the moment of reaching the ground, 

 such as dust raised by the wind, pollen of flowers, and in the 

 neighbouriiood of towns, particles of soot continually floating 

 in the atmosphere. It therefore requires great care to avoid 

 coming to erroneous conclusions respecting the nature of the 

 body under examination, and also to detect the existence of 

 organic particles in the midst of others which mask its pre- 

 sence. For these reasons I avoid entering any further upon 

 this subject at present, although deposits of rain-water have 

 presented under the microscope several particles of an organic 

 nature. 



The most prevailing forms which the particles of snow in 

 flakes assume, are minuteacicular crystals irregularly grouped 

 together, small regular rhombic prisms, often modified by se- 

 condary planes, and double six-sided pyramids, like the cry- 

 stals of sulphate of potash. The more regular particles are ge- 

 nerally found deposited on others more irregular, arranged in 

 wreaths and various other shapes. A globular nucleus with 

 small pyramids upon it is a frequent form in flakes of snow. 

 Separate particles of snow affect much more regular forms. In 

 these the hexagonal form, or some tendency to assume it, is 

 generally remarked; and examples of all the forms given in 

 Scoresby's voyage, and of others still more complex, may be 

 detected by the microscope in snow of this climate. The 

 spongy deposit formed on the outside of vessels containing a 

 freezing mixture is found under the microscope to present 

 crystalline forms, which resemble the common forms found in 

 snow much more than those of any other deposit, such as 

 frost, or the arborescent deposit often found on the windows 

 in winter. 



In these experiments the hygrometric conditions of the 

 atmosphere, the degree of refrigeration, and even the rapidity 

 with which heat was abstracted, appeared to exert great influ- 



