1894.] Presents. 115 



VI. Literature. 1. In 1697 Camerarius described, amongst hexa- 

 gonal plates of hoar frost, some slightly depressed in the middle. 



. 2. In 1874 Krenner described and illustrated hollow hexagonal ice 

 crystals found in the ice cave of Dobschau. His remarks on their 

 formation and attachment are, however, quite at variance with our 

 observations. 



3. In 1889 Assmann described and illustrated the forms of hoar 

 frost; but his illustrations only show flat fronds growing. in one 

 dimension. 



VII. -Conclusions. 1 . Water, when changing direct from the gaseous 

 into the solid state, is highly crystalline. 



2. The tendency to crystallisation is so strong that* in those cases 

 where the area of supply is limited by a wall or other heterogeneous 

 surface, skeleton crystals hexagonal "hoppers" are formed, grow- 

 ing away from that wall, even under circumstances of excessively slow 

 growth. 



. 3. Calmness of air seems to be an essential condition for their 

 formation. 



4. The natural example of crystallisation of water limited to 

 certain directions is given in hoar frost, showing a very marked 

 tendency to form hexagonal hoppers. 



5. From our observations, there can be no doubt as to the identity 

 of the ice crystals of Surtshellir, of the refrigerating chambers and 

 ships in Liverpool, and of the cooling cellars of the Berlin breweries, 

 with natural hoar frost. 



Presents, February 1, 1894. 

 Transactions. 



Baltimore : Johns Hopkins University. Studies in Historical and 



Political Science. 12th Series. N"os. 1 2. 8vo. Baltimore 



1894. The University. 



Edinburgh : Geological Society. Transactions. Vol. VI. Part 4. 



8vo. Edinburgh 1892. The Society. 



Leipsic : Astronomische Gesellschaft. Vierteljahrsschrift. Jahrg. 



XXVIII. Heft 4. 8vo. Leipzig 1893. The Society. 



London : Pharmaceutical Society. Calendar. 1894. 8vo. London. 



The Society. 



Vienna : K.K. Zoologisch-Botanische Gesellschaft. Verhand- 

 lungen. Bd. XLIII. Quartal 34. 8vo. Wien 1893. 



The Society. 



Washington : U.S. Department of Agriculture. Experhnent 

 Station Record. Vol. V. No. 3. 8vo. Washington 1893. 



The Department. 



