2i8 DISSERTATION on the 



to appear only like a pellicle above the furface, has the confider- 

 able thicknefs that I have mentioned, concealed below the water. 

 I MAY here fubjoin fome obfervations on the condud^irfg 

 power of ice with refpedl to found. This is affirmed to be very 

 great, by the ingenious ProfefiTor of Natural Philofophy in your 

 Univerfity *. I am difpofed to accede to his opinion, from know- 

 ing, that even the unbroken and uncviltivated ground of our 

 ftepps or defarts conduds found fo well, that the CofTacks hear 

 the tread of a horfe at a great diflance, by laying their ear to 

 the ground. Experiments might be tried in this country on a 

 very great fcale. But as I have not had an opportunity of this 

 kind fmce the thought ftruck me, I fhall content myfelf with 

 giving the following extradl of a letter from a friend : " Ha- 

 " ving walked out on the ice to a great diftance from our fort 

 ** the other day, when its cannon were difcharged for the taking 

 " of Oxakow, the firfl: intimation I received of this event 

 " was, by a difagreeable ringing found from the ice, and, after 

 " fome feconds, the ufual report through the air, but not fo 

 " violent as the firft." 



Regijler of the Weather for the fix Winter Months. 

 THERMOMETER. 



Our greateft cold exceeds in general 196° of De T isle's, 

 equal to 24' below o of Fair, or 24°i of Reaum. below o, 

 and commonly obtains in January. 



Our mean cold for the fix winter months is, in the after- 

 noon, 154°, equal to 27° of Fahr. above o, or equal to 2° of 

 Reaum. below o ; Night, 162°, equal to 23° of Fahr. above o, 

 or to 7° of Reaum. below o. 



It muft always be remembered, that they are the mean de- 

 grees of cold and heat during a period of fifteen years, which 



are 



* John Robison, M.A. Profeflbr of Natural Philofophy in the Univerfity of Edinburgh. 



