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* 



similar to those at the surface ; and they are liberated by an amount 

 of motion which has been transmitted through the ice without pre- 

 judice to its solidity. The conception is helped when we call to 

 mind the transmission of motion through a series of elastic balls, by 

 which the last ball of the series is detached, while the others do not 

 suffer visible separation. 



The author proves, by actual experiment, that the interior portions 

 of a mass of ice may be liquefied by an amount of heat which has 

 been conducted through the exterior portions without melting 

 them. 



The converse of this takes place when two pieces of ice at 32 

 Fahr., with moist surfaces, are brought into contact. Superficial 

 portions are by this act virtually transferred to the centre ; and 

 as equilibrium soon sets in between the motion of the tenuous film 

 of moisture between the pieces of ice and the solid on each side of 

 it, the consequence is shown to be that the film freezes, and cements 

 the two pieces of ice together. The fourth section of the paper is 

 devoted to these considerations. 



In the fifth section a series of observations bearing upon the con- 

 ductivity of ice for heat is recorded. 



In the sixth section the influence of pressure upon ice is examined. 

 A cylinder of the substance was placed between two slabs of box- 

 wood, and subjected to a gradually-increasing pressure. Looked at 

 perpendicular to the axis, cloudy lines were observed drawing them- 

 selves across the cylinder. Looked at obliquely, these lines were 

 found to be the sections of dim surfaces which traversed the cylin- 

 der, and gave it the appearance of a crystal of gypsum whose planes 

 of cleavage had been forced out of optical contact by some external 

 force. 



The surfaces are not of plates of air, for they are formed when the 

 compressed ice is kept under water. They also commence sometimes 

 in the centre of the mass, and spread gradually on all sides till they 

 finally embrace the entire transverse section of the cylinder. A 

 concave mirror was so disposed that the diffuse light of day was 

 thrown upon the cylinder while under pressure. The hazy surfaces 

 produced by the compression of the mass were observed to be in a 

 state of intense commotion, which followed closely upon the edge of 



