Prof. Tyndall on Ice and Glaciers. 403 



day's explanation must undoubtedly be given up. But the 

 essence of that explanation seems to be that the interior portions 

 of a mass of ice require a higher temperature to dissolve them 

 than that sufficient to cause fusion at the surface. To be perfectly 

 distinct, let a beam of solar heat, or a beam from the electric 

 lamp, be sent through a massof ice. The substance breaks up into 

 those six-petaled liquid flowers which have been described else- 

 where. The flowers expand as the beam continues to act, the 

 energy of the absorbed portion of the beam being almost wholly 

 expended in enlarging the flowers formed during the first few 

 seconds of exposure, and not in forming new flowers. Now 

 the assumption involved in Faraday's theory is, that, before a 

 flower makes its appearance in the interior, the ice there must 

 have been raised to a temperature higher than 0° C, while at the 

 surface the ice fuses at this temperature. When therefore two 

 moist surfaces of ice at the temperature 0° are pressed together, 

 and when, in virtue of the contact action assumed by Faraday, 

 the film of water between them is°frozen, the adjacent ice (which 

 is now in the interior, and not at the surface as at first) is in a 

 condition to withdraw by conduction, and without prejudice to 

 its own solidity, the small amount of heat set free. Once grant- 

 ing the contact action claimed by Faraday, there seems to be no 

 difficulty in disposing of the heat rendered sensible by the free- 

 zing of the film. 



When the year is advanced, and after the ice imported into 

 London has remained a long time in store, if closely examined, 

 parcels of liquid water will be found in the interior of the mass. 

 I enveloped ice containing such water-parcels in tinfoil, and placed 

 it in a freezing-mixture until the liquid parcels were perfectly 

 congealed. Removing the ice from the freezing- mixture, I placed 

 it, covered by its envelope, in a dark room, and found, after a 

 couple of hours' exposure to a temperature somewhat over 0° C, 

 the frozen parcels again liquid. The heat which was sufficient 

 to fuse this interior ice, passed through the firmer surrounding 

 ice without the slightest visible prejudice to its solidity. But if 

 the freezing temperature of the ice-parcels be 0° C, then the 

 freezing temperature of the mass surrounding them must be 

 higher than 0° C, which is what the explanation of Faraday 

 requires. 



In a former paragraph I have attached to the description of a 

 precaution used by Professor Helmholtz the query " why ? " 

 He states that water freed of its air sinks, without freezing, to a 

 temperature far below 0° C. ; while when a piece of ice is in the 

 same water it cannot so sink in temperature, but is invariably 

 deposited in the solid form at 0° C. This surely proves ice to 

 possess a special power of solidification over water. It is need- 



