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The Museum Gazette 



action of air-currents aided, of course, by the tendency of 

 the moisture to gravitate downwards. If there be a crack 

 in the pane, or a chink in the framework-fitting, there will 

 occur a quiet air-current which may dry up the moisture at 

 any part and which will distribute the moisture-charged air 

 over other parts. The projecting bars of the window frame, 

 the window curtains, and any objects in any degree shading 

 the window will have their influence, and it must be remem- 

 bered that in all rooms there is a flow of the warmer air 

 upwards. To the combined influence of all these, the cor- 

 ruscations of ice films which so delight us on drawing the 

 blinds in the morning are to be attributed. It may in any 

 particular case need some perseverance and ingenuity to trace 

 out in detail the explanation of all that is there, but this is 

 to be done on the lines which we have pointed out. 



In neglected rooms in town houses somewhat similar feats 

 of arrangement are occasionally accomplished by dust, but 

 the conditions are not precisely parallel. The dust is usually 

 blown upwards from below, and under the influence of 

 currents it forms columns which have their apices pointing 

 upwards, but it never, of course, in the least rivals the crystal- 

 line figures due to frost. 



"Jet Black Ice." 



Canon Rawnsley, in the Times of February 5, wrote from 

 Keswick : " Three nights of frost varying from 14 to 22 

 degrees, have given us jet black ice from one end of Derwent- 

 water to the other." The appearance of blackness in ice is 

 of course, an illusion, as the Canon doubtless knew well. It 

 is produced when the ice is perfectly smooth and the water 

 of great depth. Under such conditions the ice is beautifully 

 transparent both on its surface and in its structure, and per- 

 mits of vision into the black depths below. We have had a 

 remarkable succession of what are known as "black frosts" 

 this winter. 



