336 Prof. Tyndall on some Physical Properties of Ice. 



them and the atmosphere, the apparent bubbles suddenly collapsed, 

 and no trace of air rose to the surface of the warm wate)\ 



10. This is the result which ought to be expected. The 

 vohxme of water at S2° being less than that of ice at the 

 same temperature, the formation of each flower ought to be 

 attended with the formation of a vacuum, which disappears in 

 the manner described when the ice surrounding it is melted. 



Similar experiments were made with ice in which true air- 

 bubbles were enclosed. When the melting liberated the aii', the 

 bubbles rose slowly through the liquid and floated for a time 

 upon its surface. 



1 1 . Exposure for a second, or even less, to the action of the 

 sun was sufficient to develope the flowers (4) in the ice. The 

 first appearance of the central star of light was often accompanied 

 by an audible clink, as if the substance had been suddenly rup- 

 tured. The edges of the petals were at the commencement de- 



finitely curved thus, 1 ; but when the action was per-- 



mitted to continue, and sometimes even without this, when the 

 sun was strong, the edges of the petals became serrated thus. 



the beauty of the figure being thereby augmented. 



Sometimes a number of elementary flowers grouped together 

 to form a thickly-leaved cluster resembling a rose. Here and 

 there also amid the flowers a liquid hexagon might be observed ; 

 but such were of rare occurrence. 



12. The act of crystalline dissection, if I may use the term, 

 thus performed by the solar beams, is manifestly determined by 

 the manner in which the crystalline forces have arranged the 

 molecules. By the abstraction of heat the molecules are enabled 

 to build themselves together : by the introduction of heat this 

 architecture is taken down. The perfect symmetry of the flowers, 

 from which there is no deviation, argues a similar symmetry in 

 the molecular architecture ; and hence, as optical phaenomena 

 depend upon the molecular arrangement, we might pronounce 

 with perfect certainty from the foregoing experiments, that ice 

 is, what Sir David Brewster long ago proved it to be, optically 

 speaking, uniaxal, the axis being perpendicular to the sui-face of 

 freezin"-. 



