1858.] on some Physical Properties of Ice. 455 



desirous of examining how the interior of a mass of ice was affected 

 by a beam of radiant heat sent through it, he availed himself of the 

 suimy weather of last September and October. The sunbeams 

 being condensed by a lens, the concentrated beams were sent 

 through slabs of ice, the arrangement being usually so made as to 

 cause the focus to fall within the substance. The path of such a 

 beam through the ice was observed to be instantly studded with 

 lustrous spots, which increased in magnitude and number as the 

 action continued. On examining the spots more closely, they 

 were found to be flattened spheroids, and around each the ice 

 was so liquified as to form a beautiful flower-shaped figure, 

 possessing six petals. F'rom this number there was no deviation. 

 At first the edges of the liquid leaves were clearly defined ; but a 

 continuance of the action usually caused the edges to become ser- 

 rated like those of ferns. When the ice was caused to move 

 across the beam, or the beam caused to traverse different portions 

 of the ice in succession, the sudden generation and crowding together 

 of these liquid flowers, with their central spots shining with more 

 than metallic brilliancy, was exceedingly beautiful. 



A slab of ice was prepared, and placed in front of an electric 

 lamp : by a lens placed in front of the slab, the latter was pro- 

 jected upon a screen ; on sending a beam from the lamp through 

 the ice, the formation of the flowers was rendered visible to the 

 audience. 



In almost all cases these flowers were formed in planes parallel 

 to the surface of freezing ; it mattered not whether the beam tra- 

 versed the ice parallel to this surface, or perpendicular to it. 

 Some apparent exceptions to this rule were found, which will form 

 the subject of future investigation. 



The general appearance of the shining spots at the centres of 

 the flowers was that of the bubbles of air entrapped in the ice : to 

 examine whether they contained air or not, portions of ice con- 

 taining them were immersed in warm water. The ice surrounding 

 the cavities melted, the latter instantly collapsed, and no trace of 

 air rose to the surface of the water. A vacuum, therefore, had 

 been formed at the centre of each spot ; due, doubtless, to the well- 

 known fact that the volume of water in each flower was less than 

 that of the ice, by the melting of which the flower was produced. 



The associated air-and-water cells, found in such numbers in 

 the ice of glaciers, and observed by the speaker in lake ice, were 

 next examined. Two hypotheses have been started to account for 

 these cells. One attributes them to the absorption of the sun's heat 

 by the air bubbles, and the consequent melting of the ice which 

 surrounds them. The other hypothesis, which is a very reasonable 

 one, supposes that the liquid in the cells never has been frozen, but 

 has continued in the liquid condition from the neve or origin of the 

 glacier downwards. Now if the water in the cells be due to the 

 melting of the ice, the associated air must be in a rarefied condi- 



