85OW. 



lat. 2V S., which is stated by Humboldt to amount to 277 inches, 

 more than double the annual quantity hitherto observed elsewhere. 



70. The physical conditions which determine the production of 

 Know are not ascertained. It is not known whether the flakes as 

 they fall are immediately produced by the congelation of con- 

 densed vapour in the cloud whence they first proceed, or whether 

 being at first minute particles of frozen vapour, they coalesce with 

 other frozen particles in falling through the successive strata of 

 the air, and thus finally attain the magnitude which they have on 

 reaching the ground. 



The only exact observations which have been made on snow 

 refer to the forms of the crystals composing it, which Captain 

 Scoresby has observed with great accuracy in his " Polar Voyages," 

 and of which he has given drawings. The flakes appear to consist 

 of fine needles, grouped with singular symmetry. A few of the 

 most remarkable forms are represented in fig. 2. 



Fig. 2. 



71. The physical causes which produce that formidable scourge 

 of the agriculturist hail are uncertain. Hypotheses have been 

 advanced to explain it which are more or less plausible, but which 

 do not fulfil the conditions that would entitle them to the place of 

 physical causes. 



72. In the absence of any satisfactory explanation of the pheno- 

 menon, it is important to ascertain with precision and certainty 

 the circumstances which attend it, and the conditions under which 

 it is produced. 



It may then, in the first place, be considered as certain that the 



95 



