218 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 conducting 

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

 great, by the ingenious ProfefTor of Natural Philofophy in your 

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

 ing, that even the unbroken and uncultivated ground of our 

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

 the tread of a horfe at a great diftance, 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 fince the thought (truck me, I fhall content myfelf with 

 giving the following extract 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 firft 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." 



Kegijler of the Weather for the fix Winter Months. 



THERMOMETER. 



Our greateft cold exceeds in general 196 of De I isle's, 

 equal to 24 below o of Famr. or 24°^ of Reaum. below 0, 

 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. 



