194 Scientific Intelligence — Meteorology. 



the earth, and closes up all the communications between the extre- 

 mities of the crevices and the external air, and no current can take 

 place. In this manner the influx of the intensely cold air into the 

 cavern, and its ascent through the fissures, is prevented, and then full 

 play is given to the calorific power of the wave of heat which con- 

 tinues to arrive in the cavern through its rocky sides during the 

 whole continuance of winter, and communicates the warmth recorded 

 by Mr Murchison. In the beginning of summer the snows melt, and 

 the terminations and ramifications of the fissures have their commu- 

 nication with the atmosphere restored. The currents, as already de- 

 scribed, are re-established, and all the paradoxical phenomena to 

 which they give birth present themselves in due succession. 



3. Division of Seasons, of Demerara and Essequibo, British 

 Guiana. — The Seasons, which only consist of two, are divided into 

 The greater and lesser wet, — and 

 The greater and lesser dry. 



The greater or longer dry season commences in July, and con- 

 tinues until November; the range of temperature, as shewn at this 

 period by the thermometer, is from 80° to 90°, sometimes 91^ (but 

 very seldom) in the shade. 



From the severe and long-continued drought existing at this sea- 

 son, and consequent want of moisture in the atmosphere, the earth 

 becomes sterile and unproductive, and the progress of vegetation be- 

 comes as much suspended as it does during the winter in the more 

 northerly latitudes. 



It is a singular circumstance, but not less singular than true, al- 

 though not noticed by any author, that during the continuance of the 

 long dry season, night-dews are of rare occurrence. 



The short dry season extends from February to April, or Easter. 



The greater wet season then begins and continues, generally speak- 

 ing, during April, May, June, and not unfrequently part of July. 



The lesser wet season commences in December, and continues un- 

 til February. 



According to Count Robert H. Schomburgk's estimate, " the 

 mean temperature for the year is 8P 2' ; the maximum 90° ; the 

 minimum 74.°" 



Georgetown is situated in lat. 6° 49' 20" N. ; and long. 58° 1 1' 30" 

 N. 



P. S. — The coldest and most unhealthy wind is that which blows 

 from the north-west. I invariably suffered from headache, and other 



