*io DISSERTATION on the 



This circumflance of the weft and foutherly winds prevail- 

 ing during the fevere northern winter, muft. appear rather lin- 

 gular to mod people, efpecially in Great Britain, where the very- 

 name of N. and N. E. winds conveys the idea of cold. But 

 this phenomenon may eafily be explained on the principles ad- 

 vanced by ProfefTor Robison, in the Notes to Dr Robertson's 

 Hiltory of America. Vide Note 4. B. IV. 



Mean Quantity of melted Snow and Rain. 



These together do not amount, in the fix winter months, to 

 more than about five Paris inches, although the whole furface 

 of the northern countries is covered with fnow to a confiderable 

 depth, over which we drive in fledges, without diftinguifhing 

 between land and water ; whilft, during fummer, a period 

 apparently fair in comparifon, there falls more than double the 

 quantity of rain ; but indeed, as it pours in torrents, when it 

 does rain, like thunder-fhowers in hot feafons, there muft fall 

 more than the apparent drynefs of the feafon would lead one 

 to fuppofe at firft fight, efpecially when the large portion fur- 

 nifhed by the heavy night-dews, is added to the quantity. 



I must here obferve, that water feems to acquire fome 

 new properties, from being converted into fnow, fro ft, in- 

 cruftations, and even common river ice, if we are to judge 

 from the following facts : Firft, I have fhewn, in a paper pu- 

 blifhed in the Philofophical Tranfactions of London, that the 

 frozen incruftation, which is formed on the infide of the win- 

 dows, in the habitations of the lower clafs of people in this 

 country, during the fevere part of wir>ter, (an inconvenience 

 avoided in the better fort of houfes by double windows), fets 

 loofe, on thawing, a fpecies of mephitic air, producing all the 

 dangerous effects of the fumes of charcoal on people expofed to 

 its action, 



idly,. 



