28 CONTRIBUTIONS TO THE NATURAL HISTORY OF ALASKA. 



70 per cent, reaches its maximum extended period in winter, where for months the record of sat- 

 uration is not broken. This is further proven by the fact that a piece of ice half an inch in thick- 

 ness will be two mouths clinging to an erect pole. The least amount of vapor iu the air is recorded 

 from 11 a. m. to 3 p. in., or corresponding to the maximum heat for the day. 



This is, I believe, somewhat at variance from the usually assumed rule. 



The humidity of the various surface-currents also presents great differences. The northeast 

 current contains least humidity, though this wind, being the most frequent, presents many 

 irregularities. 



Following the card of winds to the south, the humidity increases, while south-southwest 

 diminishes to a slight degree. From north back to southwest the humidity increases. Of all the 

 winds, the southwest contains the greatest amount of moisture, aud is sure to result in rain or fog 

 in summer if the wind should back. To this the month of June, 1877, presented some exceptions. 



The wind blew from the southwest during the night, laden with moisture, and backing the fol- 

 lowing morning to north or northeast (a warmer wind), brought on fog as a thin stratum, though 

 not at any time as it was in former years. 



RAIN. 



Rain usually begins, with low, foggy clouds, precipitating small drops, and generally increasing 

 in size to the middle of the shower, then decrease to taper off a longer time than beginning. Mists 

 to moderate is the usual character of the showers. Hard dashes seldom occur, and then never 

 with that violence that seems to fall on the mainland but few miles distant, or in warmer countries. 

 Shower after shower hangs in the neighborhood, rarely approaching within 2 or 3 miles, and 

 carried to either side, generally to the west. Thunder and lightning seldom accompany these 

 showers. Only once has a shower, accompanied by vivid lightning aud loud thunder, passed over- 

 head, and then rivaled a thunder-storm of the Middle States. Thunder is sometimes heard in the 

 neighborhood, though not more than three or four times on an average in a year. Lightning is 

 yet rarer. The greatest amount of rain usually falls in August, and for any one day the greatest 

 recorded depth is .83 inch, while showers are frequent that give .1 to .3 inch. 



Rain occurs every December upon the winter solstice. The exposed thermometer has read 24°, 

 while rain during this period occurred. 



Hail from a heavy cumulo-stratus cloud has twice fallen, and was restricted to an area of prob- 

 ably less than 3 square miles. No visible electric display accompanied these falls. The latest 

 rains that fall are frozen the instant they touch the earth, these occurring in October or November. 



I have thought that it is probably a provision of nature to overload the weeds aud grasses to 

 break them to the ground, that the seeds may be more protected from cold by the approaching 

 winter's snow. 



SNOW. _ 



Snow usually falls in moderate quantities. A depth of over a foot has occurred but twice in 

 three years. A hard wind, generally accompanies the storm, so that it is usually drifted the instant 

 it touches the ground. It may fall in any month but July. 



Once the old and new snow met on the highest hilltops. Varied forms of flakes are met, but 

 usually the compound flakes are precipitated upon a high temperature, while the smaller kinds 

 fall during cold. Often fine flour- like particles are sifted from a thin veil of cirro-stratus and thin 

 stratus; this rarely exceeds one-tenth of an inch in depth. During clear weather frost-crystals sift 

 from the sky and can only be recognized by looking over the top of a building while the comb of 

 the roof hides the sun. It is probable that the greater part of these frost films do not reach the 

 ground, as all my endeavors to collect them on black paper in a situation well guarded against 

 currents of air were fruitless. Sometimes when a crust is formed on the snow, the heat absorbed 

 into the earth through the snow liberates vapor, which, emerging through the snow, is crystallized 

 in long spiculse like a forest of feathers, minature ferns, and palm leaves. 



In February, 1875, I noticed a V-shaped halo on the ice below me, and extending a great 

 distance, regularly diverging with the apex toward me. I now venture to suggest that these 

 frost-crystals on the ice might produce such refraction and reflection. 



