ISOCRATES 



3073 



ISOTHERMAL LINES 



ISOBARIC LINES, SHOWING DAILY AVERAGES FOR A YEAR 



ISOCRATES, isok'rateez (436-338 B.C.), 

 born at Athens, was one of the ten notable 

 orators of Attica, and was distinguished as a 

 teacher of rhetoric and oratory. Twenty-one 

 of his orations are still in existence; they are 

 remarkable for their polished style and careful 

 construction. Isocrates was the first to recog- 

 nize the value of oratory in public life. 



ISOTHERMAL, isothur'mal, LINES, or 

 ISOTHERMS. The word isotherm, which 

 meajis equal heat, is the name applied to lines 

 drawn upon maps to connect places having the 



same average temperature. To construct a 

 monthly isotherm map, the geographer must 

 average all the temperatures observed during 

 the month to find the mean temperature for 

 the month and connect the places having the 

 same average. The average temperatures of 

 the year would similarly furnish the basis for 

 a yearly map. Since places having the same 

 latitude often vary in temperature (see CLI- 

 MATE), isothermal lines are extremely irregular. 

 This is true especially of those in the northern 

 hemisphere, where the great land masses are 



120 160 160 120 80 40 



40 



40 



120 



ISOTHERMAL LINES, SHOWING DAILY AVERAGES FOR A YEAR 



193 



