PHYSICAL PROPERTIES OF ICE. 651 



During the spring of 1847, at Repulse Bay on the Arctic shores 

 of America, I was surprised to observe, after the thaw commenced, 

 that large boulders (some of them 3 or 4 feet in diameter) began to 

 appear on the surface of the ice ; and after a while, about the month 

 of July, they were wholly exposed, whilst the ice below them was 

 strong, firm, and something like 4 feet thick. 



There were no cliiFs or steep banks near from which these 

 boulders could have come ; and the only way in which I could 

 account for their appearance, was that which by subsequent 

 observation I found to be correct. 



On the shores of Repulse Bay the rise and fall of the tide are 

 6 or 8 feet, sometimes more. When the ice is forming in early 

 winter, it rests, when the tide is out, on any boulders, &c. that 

 may be at or near low-water mark. At first, whilst the ice is weak, 

 the boulders break through it ; but when the ice becomes (say 

 2 or 3 feet) thick, it freezes firmly to the boulder, and when the 

 tide rises, is strong enough to lift the boulder with it. Thus, once 

 fastened to the ice, the stone continues to rise and fall with the rise 

 and fall of each tide, until, as the winter advances, it becomes 

 completely enclosed in the ice, which by measurement I found to 

 attain a thickness of more than 8 feet. 



Small stones, gravel, sand, and shells may be fixed in the ice 

 in the same way. 



In the spring, by the double eiFect of thaw and evaporation, the 

 upper surface of the ice, to the extent of 3 feet or more, is removed, 

 and thus the boulders, which in autumn were lying at the bottom 

 of the sea, are now on the ice, while it is still strong and thick 

 enough to travel with its load, before favourable winds and cur- 

 rents to a great distance. 



The finding small stones and gravel on ice out at sea does not 

 always prove that such ice has been near the shore at some time 

 or other. 



I have noticed that wherever the Walrus in any numbers 

 have been for some time lying either on ice or rocks, a not 

 inconsiderable quantity of gravel has been deposited, apparently a 

 portion of the excreta of that animal, having probably been taken 

 up from the bottom of the sea and swallowed along with their 

 food. 



6. Some Experiments with Sea-water, by Dr. F. Guthrie. 

 (From the Proceedings of the Physical Society.) 



Sec. 32. Freezing Sea-ivater. — The sea- water with which the 

 following experiments were performed was procured from Dover. 

 After filtration, it was found to have at 760 millims. the boiling 

 point 100° "6 C, while the temperature of its vapour was 100° '2. 

 This sea- water began to freeze at —2° C. On evaporation on a 

 water-bath and keeping at 100° C. for two hours, the per-centage 

 of solid residue was 6 • 5786. A large beaker of this sea- water was 

 A tin vessel was supported inside the beaker so 



