ai6 DISSERTATION on the 



fouthern country, it would merit that appellation under the fame 

 circumftances. 



Duration of Frojl and Snow. 



The duration of winter, if it is to be defined by the mean 

 term of frofl and fnow, according to the common method, muft 

 be dated from the 9th of Odober to the beginning of May, 

 when its force is fo far fpent as to be perceptible only by a 

 flight hoar-froft at an early morning hour ; and as the continu- 

 ance of fnow is generally much the fame as that of froft, we 

 may reckon the mean period of both at about 230 days in the 

 year. 



Ter7n of the Rivers remaining Frozen. 



But the duration of what is called the real Rvifllan winter, 

 when our communication by water with the reft of the world 

 is fhut up, and that element confounded in appearance, and 

 almoft in folidity, with the land, is confiderably fhorter, and 

 is to be reckoned from the 27th of November to the 19th of 

 April, (its mean term for fifteen years paft), that is to fay, it 

 comprehends about 1 60 days in the year ; for in the feafon al- 

 lotted to winter by the ordinary definition, as given above, 

 there are about 70 days, when our froft, although equal to the 

 congelation of water in its tranquil ftate, is incapable to arreft 

 the rapid current of rivers. Nay, I am yet to learn what de- 

 gree of it might be required for that purpofe ; for in this 

 country there are certain circumftances which ufually accelerate 

 the congelation of rapid rivers, fuch as, their furface being 

 covered with floating ice, formed in the lakes * above, which, 



at 



* As for example, the floating ice which covers the Neva, and (b much facilitates its 

 congelation, is formed in the Ladoga lake, where an inferior degree of froft can aft upon, 

 the ftill water, to what is neceflary to congeal the river, and on the firfl wind it is brokje: 

 up and carried down by the current. 



