340 Mr. Smithson on the Crystalline Form of Ice. [May, 



judgment is pronounced by a name of celebrity ; it is adopted 

 and repeated by other names, perhaps of equal repute ; and thus 

 that which was originally a mistake, becomes a rule established 

 by authority. But on recurring to first principles, the error is 

 discovered, and truth at length prevails. 



To conclude in the words of Lord Bacon, " the harmony of a 

 science, supporting each part the other, is, and ought to be, the 

 true and brief confutation and suppression of all the smaller sorts 

 of objections." 



Article II. 



On the Crystalline Form of Ice. By James Smithson, Esq. FRS. 



(To the Editor of the Annals of Philosophy.) 



SIR, March 4, 1823. 



I have just seen a memoir in the Annales de Chimie et de 

 Physique for Oct. 1822, but published about a month ago, on the 

 crystalline form of ice. 



Mr. Hericart de Thury is said to have observed ice in hexago- 

 nal and triangular prisms ; and Dr. Clarke, of Cambridge, in 

 rhomboides of 120° and 60°. 



M. Haiiy supposed the form to be octahedral, and so did 

 Rome de ITsle ; and, if I mistake not much, there is in an 

 ancient volume of the Journal de Physique by Rozier, an 

 account of ice in acute octahedrals. 



Are these accounts and opinions accurate ? 



Hail is always crystals of ice more or less regular. When they 

 are sufficiently so to allow their form to be ascertained, and 

 which is generally the case, it is constantly, as far as I have 

 observed, that of two hexagonal pyramids joined base to base, 

 similar to that of the crystals of oxide of silicium or quartz, and 

 of sulphate of potassium. One of the pyramids is truncated, 

 which leads to the idea that ice becomes electrified on a varia- 

 tion of its temperature, like tourmaline, silicate of zinc, &.C 



I do not think that 1 have measured the inclination of the faces 

 more than once. The two pyramids appeared to form by their 

 junction an angle of about 80 degrees. 



Snow presents in fact the same form as hail, but imperfect. 

 Its flakes are skeletons of the crystals, having the greatest ana- 

 logy to certain crystals of alum, white sulphuret of iron, &c. 

 whose faces are wanting, and which consist of edges only. 



In spring and autumn ; that is, between the season of snow 

 and that of hail, the hail which falls partakes of the nature of 

 both, is partly the one and the other ; its crystals, though regu- 

 lar, are opaque, of little solidity, and consist, like snow, of an 

 imperfect union of grains, or smaller crystals. 



