254 American Association. 



the height of the tides in various phices, with the lines; of the 

 coast." 



Prof. Henry read a paper on 



SOME PHES"0MENA OF ICE. 



" He said that they were ia the habit of receiving all sorts of com- 

 munications and curiosities at the Smithsonian Institution ; and 

 more questions were put them than many very wise men could 

 hope to answer. One cold day in winter, a countryman was 

 shown into his office, who said he had travelled 20 miles to bring 

 him a curiosity. He proceeded to unpack it, and instead of an 

 animal, as he had expected, he found it to be a milkpan filled 

 with frozen water. On the top of the ice in it was a strange 

 formation, created without apparent cause. A crystal of ice pro- 

 truded from it in a slightly oblique manner, in shape almost like 

 an isosceles triangle, with its sides somewhat curved. This crystal 

 was found to be hollow. After ordering a drawing to be made of 

 it, the matter was laid aside for subsequent consideration, and not 

 again taken up until questions were subsequently put to him res- 

 pecting the cracking of ice in very cold Aveather. It was well 

 known that in the process of the solidification of melted metals, 

 and the freezing of water, the crystals are produced in the 

 direction of the surface from which the heat escapes. In the 

 freezing of the water in a vessel of this sort, the crystals run in 

 nearly horizontal lines, crossing each other at an angle of 60 de- 

 grees. The water, freezing first from the sides and bottom of 

 the vessel, left in the centre and top a triangular space, which the 

 yet unfrozen but expanding water found too small for it. It rose 

 above the level of the ice, therefore ; its edges freezing there 

 again, the same phenomenon recurred, and the crystal was built 

 ' up. Ice having once been formed, however, followed the law of 

 all other bodies, contracting with cold and expanding with heat. 

 Thus it was that in very cold weather the ice was found to crack 

 open sometimes with a loud report, the cracks taking place in the 

 parts of least resistance, generally the narrowest portion of the 

 body of water frozen over. The crystals formed on the surface of 

 large bodies of water in the process of freezing were nearly per- 

 pendicular, the cooling surface being that exposed to the cold winds* 

 This was easily seen as the ice decayed, and the crystals separated the 

 one from the other, The subsequent expansion of the ice by the 

 recurrence of warm v/eather sometimes brought the edges of the 

 fissures together, and crushed the newly-formed ice into a heap or 



