W. 2 1, 1880] 



NATURE 



589 



(culiar property of ice he gave the name of regelation. 

 he true explanation of this property was not at once 

 rived at. From theoretical considerations Prof. James 

 homson was led to predict that the application of pres- 

 |re to ice would lower the temperature of its melting- 



a copper wire a heavy weight. It is found that in the 

 course of a few hours the weight will have dragged the 

 wire through the ice, as if it were no harder than a piece 

 of cheese, yet that the ice has healed up as fast as the 

 wire cut into it, and that it is still one solid block. This 



extraordinary fact can be accounted for in 



the following way. In the neighbourhood of 

 the wire where it passes through the ice the 

 pressures are not uniform, for just below the 

 wire the portions of the ice are under pres- 

 sure, owing to the pull of the heavy weight, 

 while immediately above the wire the ice is 

 subjected to a stress tending to draw the 

 particles asunder, or, in other words, it is 

 subjected to a pull or " negative pressure." 

 The pressure on the ice under the wire lowers 

 its melting-point, and causes very small quan- 

 tities of it to melt ; these liquid portions 

 immediately are squeezed out, and find their 

 way round the wire to the space above it, 

 where, the pressure being reduced, they again 

 freeze hard. 



Our next picture (Fig. 26) is a simple illus- 

 tration of the principle of the diving-bell. A 

 wine-glass is turned mouth downwards and 

 plunged into a jar of water. The water rises 

 up only a very little way into the mouth of 

 the wine-glass, owing to the air which it 

 contains. The deeper the wine-glass is 

 plunged the more is the air compressed and 

 the higher does the water rise in the minia- 

 ture bell. To compress the contained air into 

 )int, and cause it to melt even though as cold as, or \ one-half of its original volume it would be necessary to 

 ilder than, the usual "freezing-point." This prediction plunge the wine-glass about thirty-four feet deep into water; 

 is afterwards verified by Sir William Thomson, who for to halve the volume of the air inside we must double 

 elted ice by subjecting it to great pressure. More the external pressure. The pressure of the air is already 



cently Mr. James Bottomley has devised a very beau- about fifteen pounds on every square inch, and to double 



ul experiment on regelation which requires no special that pressure requires the additional weight of thirty-four 



paratus for its performance. A block of ice (Fig. 25) feet of superincumbent water, for that is the depth at 



placed upon a suitable support, and over it is hung by which the water itself presses with a force of fifteen 



