INTRODUCTION. 



eastern coasts of America. The daily oscillations of the barometric 

 column, and variations of the thermometer, at Vancouver, with that 

 at Cambridge, Mass., are brought together on the same diagram, Plate 

 XVIII., page 568, by which it will be seen that the diurnal range at 

 Cambridge is much greater ; the means are nearly equal, Cambridge 

 being 67-07, Vancouver 66 ; through the diagrams of Nisqually and 

 San Francisco the observations may be compared in like manner. 



The greatest height to which the thermometer rose at Vancou- 

 ver during the mouths of June, July, and August, was 98, and it 

 fell to 39. The barometric column at Vancouver stands higher 

 than at Cambridge, though it is not subject to as great a range; 

 its mean standing was 30-203 in., that at Cambridge being 30-027 

 in., and greatest oscillation l - 372 in. The situation of Vancouver 

 differs in many respects from that of Cambridge ; it is inland, while 

 Cambridge may be said to be on the sea-coast. Vancouver is in 

 the neighbourhood of high mountains capped with snow. One is as 

 yet surrounded by a virgin forest, while the other is entirely cleared 

 and cultivated. The winds, during the time of the comparison, were 

 from the ocean; the relative time of the observation during the day 

 was the same; the absolute time only differed as in the longitude of 

 the two places. If it be desirable to get the latter, by removing the 

 Vancouver projection one-third forward, they will be almost identical 

 as to time. The state of the weather during the time the compari- 

 sons were in progress was fine, no extraordinary changes having 

 taken place. 



The winds in the western and middle section of Oregon, in the sum- 

 mer, prevail from the west and southwest; while, in the winter, they 

 blow from the southeast, to which latter circumstance the mildness of 

 the climate is to be imputed during that season. Little rain falls 

 from March to November, but from November till March rain is fre- 

 quent, though not heavy. Snow seldom falls in the western section : 

 when it does, it lasts but a short time. The nearer the coast, the 

 milder is the climate. The mean temperature at Astoria, as shown 

 by that of a bottle of water buried six feet deep, from September 6th 

 to October 1st, was 54 Fahrenheit : this I should think would very 

 nearly represent the mean annual temperature, only 1 above the 

 eastern section, yet a totally distinct climate. 



The westerly winds, in passing into the interior, lose their moisture 

 by condensation on the eastern range ; imbibe it in passing over the 

 middle section, and again it is condensed on the mountains of the 



