24 CIRCULAR OR ANGULAR MEASURE. 



degree is divided into 60 minutes, and the minute into 60 

 seconds. The length of a degree, minute, or second, de- 

 pends on the size of the circle. If the size of the circle is 

 increased or decreased, the length of the degree, minute, 

 or second is also increased or decreased. 



3. The greatest circumference of the earth's surface is 

 about 24,930 miles ; 1 of that circumference is one 360th 

 of 24,930 miles, which is 69 J miles. 



4. A geographical or nautical mile is equal to V of the 

 earth's greatest circumference, which is found to be a little 

 more than one statute mile and 49 rods. 



5. Latitude is measured north or south from the equator 

 on any meridian, and is expressed in degrees, minutes, and 

 seconds ; thus, 43 17' 31" north lat. denotes a position 

 43 17' 31" north from the equator. 



6. The linear extent of a degree of longitude depends 

 upon the latitude, and diminishes as the latitude increases ; 

 thus, at latitude 10 its extent is 359640 feet ; at lat. 40 

 it is 280106 feet ; and at lat. 80 it is only 63612 feet. 



