1-818.] Distribution of Heat over the Globe. 181 



will give us more correct results. Some very valuable observa- 

 tions have been made by noticing the thermometer from hour to 

 hour, at different seasons of the year, and in different latitudes, 

 until we are able to fix upon a number which may indicate the 

 mean of the day. Serene and calm weather has been chosen on 

 these occasions, and the thermometer has been carefully exa- 

 mined in this way, both in the observatory at Paris, and under 

 the equator. These observations have tended to confirm the 

 opinion that has been mentioned above, that the temperature of 

 the earth corresponds with the mean temperature of the atmo- 

 sphere, the disturbing causes nearly counteracting each other. 

 In expressing the results of the observations on mean tempera- 

 tures that have been made in various situations, it is convenient 

 not to employ the numbers that are derived from any parti- 

 cular scale, but to consider the equator as the standard to which 

 all the rest are to be referred, and to denote them all by numbers 

 which have an arithmetical relation to it. 



Having now ascertained the method of taking mean tempera- 

 tures, and of reducing them to a general expression, we may 

 proceed to examine the form of some of the isothermal lines. It 

 has been long known that the temperatures are not the same in 

 the same parallels, especially those in Europe and in America ; 

 but, from the facts that will be stated, we shall find that this 

 difference is not so great as has been imagined. By construct- 

 ing a table, in which we compare the mean temperature and 

 the latitude of different places in the continents of Europe and 

 America, we learn the amount of this difference, and we deduce 

 from this the number of degrees of latitude which we must go 

 northward in Europe in order to arrive at the same annual mean. 

 From this train of observations, we find that the isothermal line, 

 or band, which is considered as 32°,* passes between Ulea, in 

 Lapland, latitude 66° 68', and Table Bay, in Labrador, latitude 

 54*. The isothermal line, or band, of 41°, passes near Stockholm, 

 latitude 60°, and St. George's Bay, in Newfoundland, latitude 

 48°. The isothermal line, or band, of 50°, passes through Bel- 

 gium, latitude 51°, and near Boston, latitude 42° 30'. The 

 isothermal line, or band, of 59°, passes between Rome and Flo- 

 rence, latitude 43°, and near Raleigh, in South Carolina, latitude 

 36°. The direction of these lines of equal temperature gives the 

 following differences between the west of Europe and the east of 

 America : 



Latitude. Mean of West of Europe. Mean of East of America. Differences. 



30° 70-1° 66-8° 3-3 



40 63-1 54-5 8-6 



60 50-8 37-9 12-9 



60 40-0 24-0 16-0 



» The thermometrical numbers are all reduced from the centigrade scale to that 

 of Fahrenheit. In the original, the numbers on the centigrade icale are, 0°, 5 , 

 10 9 , 15°, reflectively. 



