350 Prof. Tyndall on some Physical Properties of Ice. 



At the termination of the experiment the water surrounding 

 the frustum was at a temperature of 36° F. 



49. These experiments show, that however bad the conduct- 

 ing power of ice, in comparison with other substances, may be, 

 the assumption that blocks of it which have been preserved in 

 this country through months of summer weather should still 

 possess a magazine of cold beyond that due to a temperature of 

 32°, is wholly incompatible with the physical character of the 

 substance. 



§VI. 



50. In a veiy interesting paper communicated to the British 

 Association during its last meeting, Mr. James Thomson has 

 explained the freezing together of two pieces of ice at 32° in the 

 following manner : — "Two pieces of ice, on being pressed toge- 

 ther at their point of contact, will at that place, in virtue of the 

 pressure, be in part liquefied and reduced in temperature, and 

 the cold evolved in their liquefaction will cause some of the liquid 

 film intervening between the two masses to freeze." I am far 

 from denying the operation under proper circumstances of the 

 vera causa to which ]\Ir. Thomson refers, but 1 do not think it 

 explains the facts. For freezing takes place without the inter- 

 vention of any pressure by which Mr. Thomson's effect could 

 sensibly come into play. It is not necessary to squeeze the 

 pieces of ice together; one bit may be simply laid upon the 

 other, and they will still freeze. Other substances besides ice- 

 are also capable of being frozen to the ice. If a towel be folded 

 round a piece of ice at 32°, they will freeze together. Flannel 

 is still better. A piece of flannel wrapped round a piece of ice 

 freezes to it sometimes so firmly that a strong tearing force is 

 necessary to separate both. Cotton wool and hair may also be 

 frozen to ice without the intervention of any pressure which could 

 render Mr. Thomson's cause sensibly active*. 



51. But there is a class of efi^ects to the explanation of which 

 the lowering of the freezing-point of water by pressure may, I 

 think, be properly applied. The following statement is true 

 of fifty experiments or more made with ice from various quarters. 

 A cylinder of ice 2 inches high and an inch in diameter, was 

 placed between two slabs of box-wood and submitted to a gra- 

 dually increasing pressure. Looked at perpendicular to the axis, 

 cloudy lines were seen drawing themselves across the cylinder ; 



* It might perhaps be stated generally, that those substances which 

 cause the precipitation of water from the gaseous to the liquid state, are 

 also most influential in converting the liquid into the solid. " Hemp, wool, 

 hair," are also the substances on which the so-called ground-ice is formed 

 most readily. See Arago's Report, Annuaire pour Van 1833. 



