x li v INTRODUCTION. 



each degree of latitude ; as the water became colder than the air, we 

 were immersed in dark fog for several days. All navigators, in pass- 

 ing over this track, have experienced the same effect, occasioned no 

 doubt by the warm southeast wind, which usually blows fresh, coming 

 in contact with the cold water from the northwest. On our return 

 voyage, seven months afterwards, we had less fog, the water being of 

 nearly the same degree of temperature with the air. The trade winds 

 were entered in 23 north. 



The range of the barometer was increased to -400 above 30 inches, 

 as we advanced to the north, and attained its maximum height in 45 

 latitude. The degree of moisture varied during the passage from '880 

 to '820. On our route from San Francisco to the Sandwich Islands, 

 the barometric column again decreased in altitude, the temperature 

 increased in the same ratio as on our route to the coast. The degree 

 of moisture was '745. 



NISQTTALLY, OBEGON. It will be well to remark that the climate 

 of Oregon varies much in the different sections, and therefore it will 

 be necessary to speak of all. The middle section is the extent of table 

 land lying 1200 to 2000 feet above the western section, and separated 

 from it by the Cascade Range, which is covered with snow the greater 

 part of the year, while the Blue Mountains divide it from the eastern. 

 This section differs both from the eastern and western divisions in 

 being colder and having less moisture, and in its temperature passing 

 through a greater range. 



The observations began at Nisqually, on the 12th May, and were 

 continued at the observatory until the 17th July. Nisqually is 

 situated at the head of Puget's Sound, the extreme southern limit of 

 the estuary leading south from the straits of Juan de Fuca. It lies in 

 latitude 47 12' north, and longitude 122 25' west, having the Coast 

 Range of mountains on the west, and Cascade Range on the east, the 

 latter always capped with snow. The diagram on Plate XVII., page 

 558, represents the mean daily movements of the meteorological instru- 

 ments during the above period. The variations of temperature were 

 great: from 37 to 92 in the shade, the mean temperature being 62'8, 

 that of the water 53-09; the mean solar radiation was C9'G3; the 

 maximum in the sun was 112, while in the shade it stood at 76 ; 

 this was on the 4th July. The oscillation of the barometer was -862, 

 and its mean standing reduced to 32, 30 - 040 inches. The winds from 

 the southern quarter have a tendency to depress it, while it rises with 

 northerly ones. The winds are for the most part from the southward 



