LESSONS IN GEOGKAl'HV 



37 



Tho main features of thin projection oonniut in tracing the 

 parallels in parallel straight lines, instead of representing 

 thorn by arcs of concentric circles as in the conical projec- 

 tion, and by using curved lines for the meridians, instead of 

 Htruitfht linos converging to a certain fixed point, oa in the 

 imiji'ctioiiH for maps of Kurope and Asia. 



On examination of our map of Africa, to which reference has 

 been made above, it will be seen that the meridian of 15 

 K. has been selected as the central meridian of the map, 

 which crosses the equator at right angles, but which does 

 not appear in the map itself. For this central meridian line 

 our readers may select the meridian of 15 or 20, as may 

 appear most desirable. Wo shall, however, in the following 

 ; 'tii m, take the meridian of 15 as the central meridian in 

 our map, and supposing that the majority of our students who 

 are following these lessons in Geography, and constructing maps 

 from our instructions, are working on a largo instead of a 

 email scale imagine meridians and parallels to be drawn inter- 

 mediate to those which appear in our map, so that these lines 

 would be but five degrees apart in our learner's projections, 

 instead of ten degrees as in the map ; that is to say, a parallel 

 would be drawn at every fifth degree north and south of the 

 equator, instead of every tenth degree, as in the map, and a 

 meridian at every fifth degree cast and west from the meridian 

 of 15 east from Greenwich, which we have assumed as the 

 meridian in our projection that crosses the equator at right 

 angles, instead of marking in a meridian five degrees east and 

 west of this central meridian, as in our map, and then drawing 

 meridians ten degrees apart east and west, proceeding in each 

 direction from the meridians that have been traced five degrees 

 each way from the central meridian. 



Having drawn two straight lines at right angles to each other, 

 one to represent the equator and the other the meridian of 15 

 east from Greenwich, we must, in order to draw the parallels, 

 first assume a space equal to five degrees of latitude, and set off 

 eight of these spaces north and south of the equator along tho 

 central meridian. Through the points thus marked draw straight 

 lines parallel to the equator on cither side of it. Those on the 

 north of it will represent the parallels of 5, 10, 15, 20, 25, 

 30, 35, 40 north latitude ; while those on the south of it will 

 represent the parallels of 5, 10", 15, 20, 25, 30, 35, 40 

 south latitude. If the learner wish to do so, he may delineate 

 more of tho southern part of Europe, as in our map, and more 

 of the ocean to the south of Cape Colony, by setting off more 

 spaces to the north and south of the equator ; there is, however, 

 no necessity for doing this, as it has been done in our map 

 merely for the sake of filling up a given space, namely, that of 

 a page of the POPULAR EDUCATOR. The parallels of 40 north 

 and south will serve very well as the inner line of the border of 

 the map at top and bottom, and define the limits of the map to 

 the north and south. It will now be necessary to insert tho 

 dotted lines representing the Tropic of Cancer and tho Tropic 

 of Capricorn, which must be drawn parallel to the equator 

 through points at the distance of 23 W 30' from it on either side 

 of it, north and south. 



In order to draw the meridians, because at the equator the 

 degrees of longitude are equal in length to those of latitude, we 

 must again open our compasses to the extent of the line assumed 

 as equal to a space of five degrees of latitude, and set off eight 

 of these spaces east and west, or right and left, of the central 

 perpendicular line which represents tho meridian of 15 E. 

 from Greenwich. The points thus obtained will be those through 

 which tho meridians must pass at the equator ; those on the right 

 of the central meridian being points through which tho meri- 

 dians of 20, 25, 30, 35, 40, 45, 50, 55 east from Green- 

 wich will pass ; while those to the left hand ore those through 

 which the meridians of 10, 5 east from Greenwich, 0, or the 

 meridian of Greenwich itself, and 5, 10, 15, 20, 25 west 

 from Greenwich will pass. The points through which the meri- 

 dians of 55 east from Greenwich and 25 u-est from Greenwich 

 pass may be taken as points through which to draw straight 

 lines parallel to the central meridian, to form the limits of the 

 map to the east and west and the inner lino of the border of 

 the map on either side. 



As tho distance between each meridian decreases gradually 

 from tho equator to the poles, means must now be taken to 

 determine the relative distance of every fifth meridian from the 

 central meridian along each parallel drawn in our projection. 



To do this, a diagonal scale most be constructed (as in the cane of 

 projection for the mapa of Europe and Asia) on the line -***" H 

 at first an being equal to a apace of five degrees of latitude. The 

 method of constructing this diagonal scale has been explained 

 in Vol. II., page 356. We must now torn to the table of geo- 

 graphical milea in a degree of longitude under each parallel of 

 latitude (Vol. II., page 357), and from this we find that the 

 length of a degree of longitude on the fifth parallel north or 

 south of tho equator is 59' 77 geographical miles. Opening the 

 compasses to thia extent, aa represented on our diagonal scale, 

 sot off distances along the fifth parallel of latitude north and 

 south of tho equator, on either aide of the central meridian, as 

 for as the border-line of tho map will permit, and proceed in the 

 same manner along each pair of parallels of latitude north and 

 south of the equator, ascertaining the distance equivalent to five 

 degrees of longitude under each parallel in question from the 

 table already mentioned, and opening the compasses to tho 

 proper extent in each case by aid of the diagonal scale. Tho 

 points thus found on each parallel will be those through which 

 the meridians must be traced. This may be effected by drawing 

 short straight lines from point to point in each successive paral- 

 lel to the north and south, or by means of a thin band of steel, 

 so bent that its edge may pass through every point marked for 

 the passage of each meridian across the parallels. The border 

 must now be completed, the degrees numbered, and the title of 

 the map and scales of geographical and English miles inserted, 

 after which the outline and different places may be fixed in 

 position as before. 



The following table will afford sufficient names for the con- 

 struction of a map of Africa on a small scale. If a large scale 

 be adopted, as we have advised, the latitudes and longitudes 

 may be obtained from the index of places appended to any ordi- 

 nary atlas. Our readers will often find that the latitude and 

 longitude of a place according to one index will differ from the 

 latitude and longitude assigned to the same place in another 

 index. This arises in most cases from a difference in the results 

 obtained at different times by independent observers, or some 

 different point being selected by each for making the obser- 

 vation. 



TABLE OF LATITUDES AND LONGITUDES OF PLACES in 



