64 THE POPULAR SCIENCE MONTHLY. 



cember, when the monthly means and the mean minima differ very- 

 little, but the mean maxima of Nukurs are higher by 7 and the ab- 

 solute maxima by more than 10. This is because snow rarely falls at 

 Nukurs, and a covering lasting for several days seldom occurs. In the 

 absence of snow there is nothing to interfere with the action of warm 

 winds, and, in that latitude, the sun heats the ground sensibly, even 

 in the middle of winter. 



The influence of a bed of snow on the maxima should vary accord- 

 ing as the temperature is below or above the freezing-point. In the 

 latter case, the melting of the snow, involving the absorption of heat, 

 would tend to prevent increase of temperature. Not only does it pre- 

 vent high maxima, but it keeps the temperature near the freezing- 

 point long after it has begun. This is why April is colder than Oc- 

 tober in Russia, Central Europe, Canada, and the Northern United 

 States. Farther north, for the same cause, the mean temperature of 

 May is below that of September. It can not be doubted that this 

 cause of cold, or rather this conversion of heat into melting action, is 

 proportional, all other things being equal, to the mass of snow that 

 remains on the ground. Hence, in countries having cold winters, the 

 principal obstacle to the rise of temperature in spring is found in the 

 quantity of snow on the ground, and not in the previous cold of the 

 winter. It is only in countries situated near the sea, or in the neigh- 

 borhood of large frozen lakes, that the mean temperature of the win- 

 ter has much influence on the depression of temperature in the follow- 

 ing spring and summer, because a larger quantity of ice is found in 

 such situations during cold seasons, and a greater sum of heat is neces- 

 sary to make the melting complete than in average seasons. Snow is 

 the only cause that can produce an analogous result in countries dis- 

 tant from seas and lakes. It may be concluded, from the observations 

 on these subjects, that, at the moment when the mean temperature be- 

 gins to rise above the freezing-point, everything depends upon the 

 sum of cold existing in the form of snow and ice. The greater it is, 

 the slower and more irregular will be the rise of temperature. 



The time of the coming of the snow, its depth, and its extent, 

 have also a very great influence on the beginning and duration of 

 the winter frosts ; and this influence is manifested, not only in the 

 particular spot, but in the northern hemisphere far to the south of 

 it. In short, we may say that snow gives duration to the cold, and 

 prevents a rapid rise of temperature. If we knew the exact moment 

 when a bed of snow was formed in the North in fall and winter, and 

 if we could announce it by telegraph, we might predict the time of 

 the freezing of rivers and canals, and thus serve the interests of vast 

 territories as of most of Asiatic and European Russia, Scandinavia, 

 British America, and the United States. The announcement of the 

 closing of rivers by ice, even if it were only four or five days in ad- 

 vance, would prevent the considerable losses caused by premature 



