98 



CRUISE OF STEAMER CORWIN IN THE ARCTIC OCEAN. 



continuing the remainder of the night, and in winter attaining its minimum temperature from one 

 to two hours before sunrise. A series of fine, clear evenings in November, 1879, gives the following, 

 the character of the wind being noted with each : 



In the majority of the instances given above the temperature at the time of the observation 

 was between +10° and —10°. Calm nights in June when the days are clear and warm, the layer 

 of air next the ground for a thickness of 10 to 15 feet is frequently reduced to the freezing point or 

 below, while above a sharp line of demarkation separates it from the superincumbent mass of 

 warm air. There will be frequently a difference of from G° to 10° between these layers, so 

 that a person moving along in the raw, chilling atmosphere ou the ground will, by climbing up a 

 ladder, experience the same sensation of warmth as in entering a room. This was frequently noticed 

 by Mr. Nelson when taking observations, the instrument shelter being elevated about 12 feet from 

 the ground. 



BAROMETRICAL PRESSURE. 



The mean barometer for 1878 and 1879 and 1880, taking the 7 a. in., 2 and 9 p. m. observations, 

 is 29.778 inches, the mean monthly average for the same period as follows: January, 29.709; Feb- 

 ruary, 29.841; March, 29.785; April, 29.720; May, 29.915; June, 29.817; July, 29.835; August, 

 29.732; September, 29.647; October 29.755; November, 29.635; December, 29.947. 



The lowest monthly average for any single month is 29.278 inches, November, 1878, and the 

 highest monthly mean 30.179 inches, February, 1879. The highest corrected single reading was on 

 January 3, 1880, of 31.012 inches, and the lowest 28.846 inches, November 8, 1878 (January, 1881, 

 28.808). 



The barometer appears to have a general tendency, during winter at least, to rise with a fall- 

 ing temperature and to fall with a rising temperature. The greatest barometrical range occurs 

 during the winter months, and the least in summer, the maximum range being 2.078 inches Janu- 

 ary, 1880, and the minimum .751 inch September, 1880, and the total barometrical range for the 

 four years preceding May, 1881, is from 28.808 (January, 1881) to 31.012, or 2.204 inches. As a 

 rule the barometer moves sluggishly, and it is unusual for it to rise or fall an inch in twenty- 

 four hours. 



The changes are more rapid during the winter months thau in summer. The only things 

 that may be predicted with tolerable certainty from the barometer are, in winter, a rising barom- 

 eter after or during warm weather probably indicates cold; a fall in the barometer after or during 

 cold weather generally precedes a rise in the temperature. This is uncertain, however, as the 

 change in the temperature may be simultaneous with the barometrical change, or precede it but a 

 little. A certain connection thus results between the changes in the winds and the movements of 

 the barometer, as it is a general rule that a change of wind to the north precedes a fall in the tem- 

 perature, and to the south a rise. 



Getting under way on the evening of the 17th we made the best of our way towards Saint 

 Paul's Island, where we arrived on the 21st at meridian, and after taking on board Lieutenant 

 Doty and the two seamen detailed for duty on Otter Island, a course was shaped for Ounalaska, 

 and on the evening of tlie 22d we anchored at that place in the inner harbor. 



