CONTRIBUTIONS TO THE NATURAL HISTORY OF ALASKA. 27 



imperfect as the knowledge is, and recognizing the necessity of carefulness, I shall endeavor to 

 present only facts, and leave the more important deductions to be made by those better pre 

 to undertake the task. 



The system of observations undertaken by me should not be considered perfect, as I have, in 

 a great measure, relied upon my own tact, through an inability to obtain the much-desired instruc- 

 tion and advice from the proper authority from the first to the last of my three years' stay at this 

 place. 



ATMOSPHERIC PRESSURE. 



The variability of pressure at all seasons, depending as it does on the influence of locality, is 

 sometimes greatly extended, so that a considerable district is included in the area of low pressure 

 in summer and generally local in winter, while area of high is usually more restricted. The 

 fluctuations of the barometric column are great. Usually a low barometer is preceded by a high 

 range, and vice versa. 



The oscillations, considered for a season, are much greater in winter than in summer. At 

 times the fall is regularly graduated and at others rapid in extreme, while opposed to this the 

 column is sometimes very sluggish, scarcely moving for the entire day. In the winter oscillations 

 a rise or fall of seventy-five hundredths of an inch is recorded several times. 



The average low winter pressure will be found to result more from the quick succession of 

 storms than from any other cause. Wave after wave of cold, each succeeded by one of warmer, 

 will keep the column in a state of continual oscillation. The fall is usually more noticeable and 

 extended in winter during a storm from the north or northeast than from any neighboring effect of 

 heat. 



The oscillations during a storm correspond to the variable force of the wind, and usually 

 coexistent with the greatest force of the wind. 



The extreme height of the barometer is usual in November upon the setting in of winter, 

 reading 30.9G0; a corresponding low from the increasing heat of summer in May, reading 28.701. 

 A continued maximum, when the barometer reads above 30.00, is of frequent occurrence in all 

 seasons of the year. A corresponding low prevails to a less degree. Often periods not controlled 

 by other than local influences show that the rain-fall begins at one-tenth of an inch below an 

 assumed mean of 29.700, and the column wavers upward immediately on the fall of the first few 

 drops. 



TEMPERATURE. 



The range of temperature, covering the extremes of 75° in June and — 50° in February, is 

 extremely variable for each month, and this for the different years is irregular. 



Starting from April, we find the mean monthly heat increases almost uniformly to a maxi- 

 mum mean of 55°. 355 for July and 52°.096 for August, then as steadily declines during the fall and 

 winter months, usually reaching its minimum mean in February or March. 



The minimum may occur in either of these months. During the winter the temperature is 

 subject to a greater range for each month than in summer. In Jauuarya range of 80° has been 

 recorded as the extremes for a month, and in July a range of 32° was the greatest. Ranges 

 ueaily as great as the former may occur at irregular periods during the winter. The least varia- 

 tion between the extreme means for any two days in a month is found usually in August, when 

 8°.5 is read, while the greatest variation between the extreme means for any two days in a month 

 is found in January, giving a reading of 50°. 75. The greatest monthly variation is found in July, 

 with the mean of 55°.355j and February having a mean of — 23°.8, making a difference for the 

 extremes for the months of 79°.155. That this latter is exceptional will be seen from the appended 

 summary. 



The least daily variation, derived from the maximum and minimum thermometers, shows only 



2°.5, while 4° to 5° is common. 



HUMIDITY. 



The prevailing high humidness of the air in this locality shows considerable variance between 

 the winter and summer ; in the latter reading occasionally as low as 40 per cent., and usually at 



