254 CLIMATOLOGY. 



Progress of the Seasons at Fort Franklin, on Great Bear 

 Lake, in lat. 65° 12' N., long. 123° 12' N. 



The mean temperature of the three winter months varies 

 comparatively little in different years ; but the relative tem- 

 peratures of these months differ greatly among themselves, so 

 that in one year December is the coldest month, in another 

 February, and in a third January. In some years the tem- 

 perature of places exposed to the sun rises for a day or two in 

 winter above the freezing point, and the snow moistens on the 

 surface ; but in other winters no thaw whatever occurs. 



In March the snow is deepest, and averages about three feet, 

 being, however, often drifted to a much greater thickness under 

 cliffs and on the borders of lakes. In the end of March or 

 beginning of April trees begin to thaw, the mean temperature 

 in the shade being about zero Fah. ; but the effect of the sun's 

 rays on the blackened bulb of a thermometer being sufficient to 

 raise the mercury to + 90 ° Fah. 



About the 10th of April the snow begins to thaw decidedly 

 in the sunshine, and myriads of Podurce are seen at such 

 times moving actively in its cavities. Ptarmigan begin to 

 assume their summer plumage towards the end of the month. 



From the 1st to the 6th of May, according to the season, 

 water-fowl arrive. The Colymbus glacialis and arcticus ? 

 arrive occasionally earlier, and frequent a piece of water at 

 the efflux of Bear Lake River from the lake, which remains 

 open all the year. 



Swans (Cygnus buccinator and americanus) are among the 

 early arrivals, the larger species coming first. The Anas acuta, 

 A. crecca, Clangula histrionica, and Oidemia perspicillata 

 make their appearance within the first eight days. Gulls come 

 about the 9th or 10th. Singing birds, orioles, and swifts 

 arrive about the middle of the month ; the latter varying 

 their time of appearance to a week later, if the spring is 

 tardy. Pools of water and swamps must have been thawed 

 long enough to release a sufficiency of winged insects for the 

 support of the swallow tribe, before they show themselves in a 



