170 Mr. G. Gore on the Molecular Movements and Magnetic 



The alleged limit to the thickness of a glacier. 



In his memoir " On the Mechanical Properties of Ice/' pub- 

 lished in the Philosophical Magazine for January 1870, Canon 

 Moseley arrives at a conclusion in regard to the crushing of ice 

 to which I am unable, without some qualifications, to agree. In 

 ]iis experiments ice was crushed under a pressure of 308*4 lbs. 

 on the square inch, and he concludes that if a glacier is over 710 

 feet in thickness the ice at the under surface must be crushed 

 by the incumbent weight. Professor Phillips also made some 

 experiments on the crushing of ice, and he came to the conclu- 

 sion that the height of a crushing column of ice is between 1000 

 and 1500 feet, and concluded also that if a glacier were to 

 exceed this in thickness the ice would lose its solidity*. Whether 

 the height of a crushing column of ice be 710, or 1000, or 1500 

 feet is of no consequence whatever as regards the possible thick- 

 ness of a glacier. No doubt a piece of ice solidified not under 

 pressure would be crushed to powder were it placed under a gla- 

 cier 1000 feet in thickness or so ; but after being crushed it 

 would resolidify, and would then probably be able to sustain a 

 pressure of 2000 feet of ice. This follows as a necessary con- 

 sequence from the property of regelation. There is as yet, so 

 far as I am aware, no known limit to the amount of pressure 

 which ice may sustain. There probably is a limit ; but what that 

 limit is has not yet been determined. Canon Moseley says that 

 " there is no glacier alleged to have so great a depth as 710 feet." 

 The Humboldt glacier in North Greenland, according to Dr. Kane, 

 has a depth of more than three times 710 feet. And Dr. Heyes 

 found in Baffin's Bay icebergs (which are just pieces broken off 

 the ends of glaciers) aground in about half a mile of water. And 

 on the antarctic continent we have reasons for believing that the 

 ice is in some places over a mile in thickness f. 



XX. On the Molecular Movements and Magnetic Changes in Iron 

 fyc. at different Temperatures. By G. Gore, F.R.S.X 



RW. FOX § has shown that cast iron in the melted state 

 * produces little or no magnetic effect upon a delicately 

 poised magnetic needle placed near it during its cooling, solidi- 

 fication, and subsequent further cooling, until the solid metal 

 acquires "a cherry-red colour;" it then suddenly attracts the 

 needle with great energy. Gilbert had also many years before 



* Paper on Glacial Striation read before the Geological Section of the 

 British Association, 1865. 



t Geological Magazine for June 1870, p. 2/6. 



X Communicated by the Author. 



§ Philosophical Magazine, vol. vii. (1835) p. 388. 



