FROST-FORMS ON ROAN MOUNTAIN. 



33 



application of other particles on the windward side, and by the 

 rebonnd to the lines already laid of those particles which are 

 driven violently against the surfaces between the lines. On 

 smooth, narrow bodies, as this process is continued, the deposits 

 along the sides or edges soon become so thick and long as to meet 

 in the middle. On rough surfaces new lines and centers of groups 

 are begun on all projections, however slight, and the particles re- 

 bound to them from the surrounding surfaces. 



Fig. 3, a section of rough board, illustrates this. The devia- 

 tion from the perpendicular in the frost-forms on the edges is due 



^^ to the fact that the board 



"S ^IH^^H^^I was not accurately facing 



the wind. 



There is, of course, a 

 great variety of forms pro- 

 duced in different storms, 

 all wonderful for delicacy 

 of design and perfection 

 of finish such as could 

 not be imitated in any 



Fig. 



Fig. 6. 



material. Among them may be shown a branch of balsam fir 

 {Abies Fraseri) (Fig. 4) which bears the heavy fringe of the storm 

 of December 28th, when the wind blew at the rate of fifteen to 

 twenty-five miles an hour, and the temperature was fifteen degrees 

 above zero. 



Fig. 5, a pillar and standpipe, shows the perfect fir-tijj pattern 

 of January 3d. Wind, fifteen to thirty miles an hour ; tempera- 

 ture, ten degrees below zero. The lower temperature and swifter 

 wind account mainly for the difference between this form and 

 the preceding one. The leeward sides of pillar and pipe are 

 thinly coated by the rebound of particles from the house wall. 



vor. XLV. 3 



