Extracts explanatory of the Phenomena, 4'e. 15 



succession (converging towards the centre in the form of shells 

 similar to the external sm-face), at times which will deviate 

 further from midwinter and midsummer the deeper the point 

 is in the interior, so that, at certain depths in the interior, the 

 cold wave will arrive at midsummer, and the heat wave in 

 midwinter. A cave (if not very wide mouthed and very airy') 

 penetrating to such a point, will have its temperature deter- 

 mined by that of the solid rock which forms its walls, and 

 wiU of course be so alternately heated and cooled. As the 

 south side of the hill is sunned, and the north not, the summer 

 wave will be more intense on that side, and the winter less so ; 

 and thus, though the/brm of the wave will still generally cor- 

 respond with that of the hill, their intensity will vary at differ- 

 ent points of each wave-surface. The analogy of waves is 

 not strictly that of the progress of heat in solids, but nearly 

 enough so for my present purpose. 



The mean temperature for the three winter months, De- 

 cember, January, February, and the three summer months, 

 June, July, August, for the years 1836, 7, 8, and the mean of 

 the year, are for Catherinenbourg as follows : — 



The means of the intermediate months are almost exactly 

 that of the whole year, and the temperature during the three 

 winter, as well as the three summer months, most remarkably 

 uniform. 



This is precisely that distribution of temperature over time, 

 which ought, under such circumstances, to give rise to well- 

 defined and intense waves of heat and cold ; and I have little 

 doubt, therefore, that this is the true explanation of your phe- 

 nomenon. 



