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



smooth small hail or snow not falling in flakes, but single 

 particles." The cause of this confusion arises from our in- 

 ability to give any character visible to the naked eye, appli- 

 cable on all occasions, for distinguishing hailstones, sleet, 

 and globular masses of snow from each other. In ordinary 

 cases, particularly in the summer months, no difficulty is 

 found in the use of the term hailstones. We might then de- 

 fine them as consisting generally of fragments of ice, hard, 

 nearly opake, and producing various physical effects in pro- 

 portion to their velocity ; but a more minute examination soon 

 shows, that they are generally accompanied with some suffi- 

 ciently small to deserve the name of sleet according to 

 Kaemtz, and others with no more consistency than flakes of 

 moistened snow ; and if we were to accept the definition of 

 sleet by M. Pouillet, in this country, where hail is generally 

 much smaller than in warmer climates, hail storms would be 

 of comparatively very rare occurrence. In showers of sleet 

 and snow the same difficulties are sometimes experienced ; if 

 particles of sleet invariably presented themselves under the 

 form of transparent globules or particles of ice, no possibility 

 of confusion would exist between them and the other two, but 

 we also find them sometimes mingled with some that are 

 more or less opake and possessing a greater size. This un- 

 certainty respecting the precise meaning attached to the 

 words hail and sleet, is found in the accounts of many meteo- 

 rological phaenomena ; and it would be desirable, in order to 

 avoid it, to define the exact sense in which they are employed, 

 or what would be still preferable, to describe with more 

 precision the principal physical characters presented by the 

 particles themselves. I fear it will be impossible at present 

 to propose any set of terms which in every case would be free 

 from objection, any more than with regard to the different 

 forms of clouds or other meteorological phaenomena, which 

 pass with gradual transition from one form to another; but I 

 would propose to confine the term sleet to all particles of 

 water which are transparent throughout, whatever may be 

 their size, and that of hail to those which are merely semi- 

 transparent throughout, or possess at any part the power of 

 irregularly dispersing light, which, as we shall see hereafter, 

 arises from their being composed of minute globules. The 

 term snow will be applied to all those particles of water in the 

 atmosphere in which we can detect a crystalline appearance 

 by aid of the microscope. With regard to hail, which pos- 

 sesses no cohesion and loses its form when it comes in contact 

 with any solid body, I term it amorphous hail, from its having 

 no definite form ; and the snow, whose crystalline forms have 



