Running Streams during periods of Frost. 229 



it had an opalescent hue, and there were many instances of 

 pebbles* imbedded in it, varying in size from a walnut up to 

 a stone of three inches diameter. The stream where the 

 water ran uncovered by surface-ice contained a continued 

 succession of groups of icy spiculse floating down, affording 

 an unerring indication that the bed of the river contained 

 quantities of submerged ice. A field of these spiculse had 

 collected below Eden bridge, which the severity of the wea- 

 ther soon converted into a sheet of solid ice, leaving only the 

 spiculse, which had been raised out of the water by others 

 underneath them, to attest its formation. 



These details shew that a stream must soon be cooled 

 down to 32° when its water has to bathe masses of ice in its 

 downward progress ; also that after it has attained this 

 temperature it will lodge any free crystals of ice which may 

 be borne along by the current in localities suitable for their 

 reception, without reference to the external influence of at- 

 mospheric temperature to which that part of the stream may 

 be exposed. Hence it is that under the arch of a bridge 

 ground-ice is found as abundantly as in the most open part 

 of the river. 



In the Neva, at St Petersburg, I have been told that the 

 anchor of a ship when drawn up will sometimes be found 

 to have its fluke covered with ice, which it is easy to con- 

 ceive may be the case after the long winter of Russia, when 

 a, short frost in Cumberland lodged a cubic yard of loose ice 

 in the bed of the Eden. 



On the Nature and Origin of different kinds of Dry Fogs. 

 By M. C. Martins. 



Ordinary fogs are composed of aqueous vapour in a 

 vesicular state. Their appearance, the effect they have on 

 our organs, and, in particular, the indications of hygrometrical 

 instruments, and the optical phenomena they present, leave 

 no doubt on this subject. 



There are other kinds of fogs which are quite dry. Their 



* Pebbles in rudely shaped icy barges have been described to me by parties 

 who have often watched them as they floated along on the surface of a stream- 



