OR, PLAIN TEACHING. 



47 



meridian of Greenwich, a.m., in 

 various readings, means ante-me- 

 ridian, or before the sun has 

 passed the line — before noon; p.m. 

 means 'post-meridian, or after the 

 sun has passed the line — after- 

 noon. Latitude is always rec- 

 koned either north or south, and 

 longitude always east or west. 

 Although the squares formed 

 upon the map by the intersecting 

 lines are very small, they repre- 

 sent vast areas of space. In 

 order, therefore, that smaller dif- 

 ferences of position may be de- 

 fined, the spaces between the 

 parallels, 8, and the meridians, 10, 

 are divided into degrees, 13, the 



degrees again into minutes, and 

 the minutes into seconds. The 

 equator is divided into 360 degrees 

 of longitude. As each meridian 

 divides the earth into halves, 

 there are 180 degrees of east lon- 

 gitude, and 180 degrees of west 

 longitude. These, together, make 

 up the 360 degrees. The paral- 

 lels of latitude are, in like man- 

 ner, divided into degrees, of which 

 there are 90 from the equator to 

 each pole. Degrees are marked, 

 in geographical and other read- 



ings, by a little ring, °, minutes 

 by a dash, ', and seconds by a 

 double dash, ". Thus, 29 a 25 32", 

 reads as 29 degrees, 25 minutes, 

 32 seconds. But seconds are 

 rarely referred to in ordinary 

 readings. A geographical mile 

 contains about 2025 yards ; there 

 are sixty of these miles m a de- 

 gree. The squares upon the map, 

 formed by the intersection of the 

 rieridians and parallels, generally 

 contain 360,000 square miles, or 

 four times more than the area of 

 Great Britain. But the squares 

 become smaller towards the north 

 and south, because the meridians 

 meet at the poles. For this rea- 

 son, the degrees of longitude be- 

 come less towards each pole, while 

 the degrees of latitude are every- 

 where nearly equal. For the same 

 reason, the meridians, 10, are not 

 parallel ; the latitudes, 8, do not 

 look parallel upon the map, be- 

 cause we cannot represent a round 

 body oia a plain or fiat surface 

 without curving the lines ; and as 

 the circumference of the earth 

 decreases towards the poles, some 

 lines are necessarily curved more 

 than others, thereby interfering 

 with the appearance of 

 correct parallels. But 

 the geographical pro- 

 portions are always 

 preserved within the 

 parallels, though the 

 lines deviate. On the 

 margins or borders of 

 maps there are figures 

 attached to each of the 

 parallels; these show | 

 the number of the de- 

 grees of latitude, 14. 

 There are also Hack and white 



14 



W 30 



i 20 



10 



246. 



