FROIST-FORMS ON ROAN MOUNTAIN. 



3 



be stated. The anemometer was frequently clogged by accumu- 

 lations of frost upon it. Incessant winds and flying snow dust 

 prevented the taking of clear photographs out of doors, and many 

 plates were spoiled by inexperienced handling. 



The factors in the production of these frost-forms are the 

 frozen vapor and the wind. Their size, shape, and location are 



Fig. 3. 



controlled by the amount of moisture, the temperature, the direc- 

 tion and velocity of the wind, the shape, size, and situation of the 

 objects on which they are deposited, and the size and nearness of 

 the surrounding objects. The lower the temperature, the denser 

 the cloud, the swifter the wind, and the more perfect the expos- 

 ure, the more rapid the growth and the more profuse and elab- 

 orate the results. 



Fig. 1 shows a six-sided wooden pillar with a deposit made in 

 two hours. Wind, about thirty miles an hour ; temperature, fif- 

 teen degrees below zero. Frost in the form of fir-tips, projecting 

 three quarters of an inch from the corners, and one fourth to 

 one half inch from the spaces intervening. A space two inches 

 square contained twenty-five. 



Fig. 2 shows the same pillar a week later, after five days of 

 storm and two of sunshine. Frost-forms now 2)rojecting fourteen 

 inches and glazed on outside. 



There is no fixed proportion between the size of the base of 

 the deposit and the deposit itself. It is remarkable for cohesive 

 strength, stiffness, and tenacious grip upon its base. In the case 

 of round bodies, such as trees or wires, it clasps but half the cir- 

 cumference, the other half being not even glazed (unless some 

 large object be directly to leeward), and stands out on the wind- 

 ward side of its support, following its curves and angles with 

 precision. Sometimes a tree or a grove of trees may be seen en- 

 tirely white on one side and green on the other. 



Unless there are numerous changes in the direction of the 

 wind during the progress of construction, the first aggregations 



