449 



Dr. Tyndall added to one of his papers*, a note of mine " On ice 

 of irregular fusibility " indicating a cause for the difference observed 

 in this respect in different parts of the same piece of ice. The view 

 there taken was strongly confirmed by the effects which occurred in 

 the jar of water at constant temperature described in the beginning 

 of the preceding pages, where, though a thawing process was set up, 

 it was so slow as not to dissolve a cubic inch of ice in six or seven 

 days. The blocks retained entirely under water for several days, 

 became so dissected at the surfaces as to develope the mechanical 

 composition of the masses, and to show that they were composed of 

 parallel layers about the tenth of an inch thick, of greater and lesser 

 fusibility, which layers appear, from other modes of examination, to 

 have been horizontal in the ice whilst in the act of formation. They 

 had no relation to the position of the blocks in the water of my ex- 

 periments, or to the direction of gravity, but had a fixed position in 

 relation to each piece of ice. 



ADDENDUM, received April 28. 



The following method of examining the regelation phenomena above 

 described may be acceptable. Take a rather large dish of water at 

 common temperatures. Prepare some flat cakes or bars of ice, from 

 half an inch to an inch thick ; render the edges round, and the upper 

 surface of each piece convex, by holding it against the inside of a 

 warm saucepan cover, or in any other way. When two of these pieces 

 are put into the water they will float, having perfect freedom of motion, 

 and yet only the central part of the upper surface will be above the 

 fluid ; when, therefore, the pieces touch at their edges, the width of 

 the water-surface above the place of contact may be two, three, or 

 four inches, and thus the effect of capillary action be entirely removed. 

 By placing a plate of clean dry wax or spermaceti upon the top of a 

 plate of ice, the latter may be entirely submerged, and the tendency 

 to approximation from capillary action converted into a force of 

 separation. When two or more of such floating pieces of ice are 

 brought together by contact at some point under the water, they 

 adhere ; first with an apparently flexible, and then with a rigid adhe- 

 sion. When five or six pieces are grouped in a contorted shape, as 



* Philosophical Transactions, 1858, p. 228. 



2 i 2 



