CLIMATOLOGY OF NEW HAMPSHIRE. 



131 



pure ice, which have always a pccuHar hue of greenish blue ; and there is 

 a striking contrast between this and the pure white of the frost-work on 

 the side opposite. When the tlicrmometer ranges from 25^ to 30'^, and 

 the wind is southward, ice often forms to tlie thickness of a foot or more 

 on the telegraph poles near the summit. These icy masses are formed 

 evidently by the condensation of the vapor of the atmosphere. The frost- 

 work is also formed by the condensation of vapor, but, besides the vapor, 

 the air must be filled with very minute spicul?e of ice. As the vapor 

 condenses, these are caught, and thus the horizontal, feathery masses are 

 formed. This accounts for the facts that we have observed, namely, that 

 it forms when the wind is northward, and always towards the wind. 



Fig. 16 will give a general idea of the appearance of the Tip-top house 

 when the frost-work has formed to a thickness of two or three feet on 

 the building and the rocks. 



Pifj. 16.— TIP-TOP HOUSE IN WINTER. 



The beginning of the frost-work is shown in the accompanying helio- 

 type entitled Frost Feathers. Here they are formed on the surface of a 

 rock. The longest points are ten inches in length, and each presents 



