Prof. Tyndall on some Physical Projjerties of Ice. 337 



§11. 



13. On the 25th of September, while examining a perfectly 

 transparent piece of Norway ice, which had not been traversed 

 by the condensed sunbeams, I found the interior of the mass 

 crowded with parallel liquid discs, varying in diameter from the 

 tenth to the hundredth of an inch. These discs were so thin, 

 that when looked at in section they were reduced to the finest 

 lines. They had the exact appearance of the circular spots of 

 oily scum which float on the surface of mutton broth, and in the 

 pieces of ice first examined they always lay in the planes of 

 freezing. 



1 4. As time pi'ogressed, this internal disintegration of the ice 

 appeared to become more pronounced, so that some pieces of 

 Norway ice, examined in the middle of November, appeared to 

 be reduced to a congeries of water-cells entangled in a skeleton 

 of ice. The effect of this was rendered manifest to the hand on 

 sawing a block of this ice, by the facility with which the saw 

 went through it. 



15. There seems to be no such thing as absolute homogeneity 

 in nature. Change commences at distinct centres instead of being 

 uniformly and continuously distributed ; and in the apparently 

 most homogeneous substance we should discover defects, if our 

 means of observation were fine enough. The above observations 

 show that some portions of a mass of ice melt more readily than 

 others. The melting temperature of the substance is set down 

 at 32° F. ; but the absence of perfect homogeneity, whether from 

 difference of crystalline texture or some other cause*, makes the 

 melting temperature oscillate to a slight extent on both sides of 

 the ordinary standard. Let this limit expressed in parts of a 

 degree be /. Some parts of a block of ice will melt at a tempe- 

 rature of 32— ^, while others require a temperature of 32 + ^: 

 the consequence will be that such a block raised to the tempera- 

 ture of 32° will have some of its parts liquid, and others solid. 



16. When a mass exhibiting the water-discs was examined by 

 a concentrated sunbeam, the six-leaved flowers before referred to 

 were always formed in the planes of the discs. 



17. In all my earlier experiments I found the rule to hold 

 good, that both discs and flowers were developed in the planes 

 of freezing ; but I was subsequently surprised to find, in the self- 

 same mass of ice, the discs lying in different planes. On ex- 

 amining such pieces I found them traversed by hazy surfaces of 

 discontinuity, which divided the apparently continuous mass into 

 irregular prismatic segments. When examined by allowing the 

 red light of a fire to cross it, such ice had a beautiful appearance. 



* See Mr. Faraday's Note on this subject at the end. 

 Phil. Mag. S. 4. Vol. 10. No. 108. Nov. 1858. Z 



