1818.] Distribution of Heat over the Globe. 187 



the same ; but the difference begins to be felt in the Atlantic 

 about the 22° of latitude ; and there is a considerable difference 

 between the mean temperature of Rio Janeiro and Havannah, 

 although they, are both equally distant from the equator, the 

 former being 74-5°, the latter 76'4°. The southern climates gene- 

 rally differ from those of the north in respect to the distribution 

 of the temperature through the different parts of the year. In 

 the southern hemisphere, under the isothermal lines of 46° and 

 50°, we find summers which, in our hemisphere, belong to the 

 lines of 35*5° and 41°. We are not accurately acquainted with 

 the mean temperature of any place above 50° of south latitude ; 

 but there is every reason for supposing that it differs considerably 

 from the same degree north. 



In estimating the temperature of the ocean there are four 

 circumstances particularly to be attended to ; 1 . The temperature 

 of the water at the surface, corresponding to the different lati- 

 tudes, supposing it to be at rest, without either shallows or 

 currents ; 2. The decrease of heat in the strata of water which 

 rest upon each other ; 3. The effect of shallows, or banks, upon 

 the temperature of the surface water ; 4. The temperature of the 

 currents which mix together the waters of different zones. The 

 water of the ocean is said to be the warmest between 5° 45' N. 

 and 6° 15' S. ; it has been found, by different observers, to be 

 from 82'5° to 84* 5° ; the temperature of the ocean in this part 

 is from 4° to 6° higher than the temperature of the air which 

 reposes upon it. As we advance towards the poles, the influence 

 of the seasons upon the temperature of the surface of the sea 

 becomes very sensible ; but as a great mass of water follows the 

 changes of the temperature of the air very slowly, the means of 

 the months in the ocean and in the air do not correspond. 



To complete the subject of temperature, we have still to con- 

 sider its variations in the different regions of the atmosphere, 

 and in the interior of the earth ; but our remarks have been 

 already extended to so great a length, that we shall not, at 

 present, enter upon these topics. 



Isothermal Bands, and Distribution of Heat over the Globe. 



The temperatures are expressed in degrees of Fahrenheit's 

 thermometer ; the longitudes are counted from east to west, 

 from the first meridian of the observatory of Paris. The mean 

 temperature of the seasons have been calculated so that the 

 months of December, January, and February, form the mean 

 t-.mperature of the winter. The mark * is prefixed to those 

 places the mean temperatures of which have been determined 

 with the most precision, generally by a mean of 8000 observa- 

 tions. The isothermal curves having a concave summit in 

 Europe, and two convex summits in Asia and Eastern America, 

 the climate is denoted to which the individual places belong : 



5 



