J. G. Goodchild — Motion of Land-ice. 



19 



III. — The Motion of Land-ice, 

 By J. G. Goodchild, F.G.S., of H.M. Geol. Survey, 

 Lecturer on Geology and Palseontology at the Heriot-Watt College. 



A MONGST the many useful tables given in Prof. Prestwicli's 

 JTjL " Geology " is one on the expansion and contraction of ice 

 under variations in temperature (vol. i. pp. 139 and 183). The table 

 in question is abbreviated from one of greater length, which was 

 published in the year 1845 by Carl Brunner von Wattenwyll in tlie 

 Annates de Cliimie et de Physique, 3"^ ser. tome 14, pp. 369-378, 

 under the title of " Experiences sur la densite de la glace a differentes 

 temperatures." The author of the paper referred to made an ex-* 

 tensive series of observations upon the contraction of ice under 

 various temperatures below the freezing-point ; and he proved con- 

 clusively that, under these circumstances, the contraction of ice 

 exceeds that of all other solid bodies that had (up to the date of 

 the paper) been studied in this connection. Taking the density 

 of pure water at 0° Centigrade as unity, then the contraction in 

 question for a fall of each degree Centigrade is expressed by the 

 decimal figures in the right-hand column of the following table 

 (op. cit. p. 378) :— 



In connexion with this table the author adds that the mean 

 contraction for a fall in temperature of every degree Centigrade is 

 0-0000375, or „ eloo- 



If the density of the ice increases from 0-91800 at the freezing- 

 point to 0-92025 aS the temperature falls to — 20° Centigrade, then, 

 of course, the density will diminish, or, what is the same thing, 

 the bulk will increase, proportionately, as the temperature of the 

 ice rises. 



M. Brunner's testimony does not stand uncorroborated ; for Prof. 

 Prestwich adds to his summary of the paper (Geology, vol. i. pp. 

 139, 140) some important observations by Dr. Eae upon the ice of 

 the Arctic American lakes, which bear upon the same question. 

 These observations prove, beyond the possibility of doubt, that ice 

 does contract greatly under low temperatures ; and, also, that as 

 the temperature rises towards zero Centigrade, the ice does undergo 

 a corresponding increase in volume. 



