388 



THE POPULAR EDUCATOE. 



LESSONS IN GEOGRAPHY. XXVI. 



CONSTRUCTION OF A MAP OF EUROPE (continued). 

 our last lesson we gave our readers ample instructions for 



the projection that he has made of a map of Europe, and on 

 which he is desirous of fixing the position of places given in 

 our list. First, a strip of cartridge-paper or thin Bristol board 

 must be taken, such as is represented by A B c D in Fig. 18, and 



making a conical projection of a map of Europe ; and to enable . in this an open space, abed, must be cut out with a sharp pen- 

 them to finish the map by marking in the chief geographical i knife, equal in length to nine spaces of five degrees each of the 

 features, and cities, and towns of this continent, we commence length assumed in the projection to be equal to five degrees, and 

 in the present lesson a list of the names of the principal places just wide enough to include the whole of a strip of the map 

 in Europe, the countries in which they are situated, and their from north to south contained between any two contiguous 

 respective latitudes and longitudes, so that the student may be ! meridians, which, it will be remembered, have been traced on 

 enabled to fix for himself the proper position of each in his pro- ! the meridian at the distance of five degrees of longitude apart, 

 jection, and thus learn geography in the most effective 

 manner possible, while he is at the same time ac- 

 quiring the power of constructing maps in general. 



The student must remember that the position of the 

 point (marked M in Fig. 14, page 356, and F in Fig. 

 17, page 356) from which the concentric arcs are de- 

 scribed which form the parallels of latitude in a coni- 

 cal projection, varies according to the point where the 

 circumscribing cone is supposed to touch the sphere or 

 the points where it is supposed to enter the sphere. 

 For example, it is only for the map of Europe, or for 

 any part of the zone that surrounds the sphere be- 

 tween the parallels of 35 and 75 N. latitude, that the 

 point from which the parallels of latitude are described 

 can be taken at 5 beyond the pole for projections on 

 a small scale or, more accurately, at 4 30' 30'' for pro- 

 jections on a large scale ; because, in the construction 

 of a projection for any part of the sphere lying in the 

 zone included between these parallels north and south, 

 and bounded by any two meridians east and west, the 

 circumscribing cone on which the portion of the sphere 

 to be drawn is projected, is supposed to enter the 

 sphere in the parallels of 45 and 65 N. latitude, two 

 parallels equidistant from the parallels that bound the 

 ;;one on the north and south. If the student will take 

 the trouble to draw for himself a quadrant of a circle 

 graduated from to 90 ' in spaces of 5, as in 

 Fig. 14 (page 356), and then draw a series of straight 

 lines, like L M, entering the sphere at pairs of points, 

 5, 10, 15, or 20 degrees distant from each other, as he 

 may determine, he will find that the nearer to the pole 

 are the points in which the circumscribing cone enters 

 the sphere, the less is the distance beyond the pole of 

 the point from which the concentric arcs representing 

 the parallels of latitude are to be described, and that 

 this point becomes farther and farther removed from 

 the pole as the points through which the circumscrib- 

 ing cone enters the sphere approach nearer and nearer 

 to the equator. It is evident, then, that when we are 

 making a conical projection of any portion of the 

 sphere near the equator, or any portion in higher lati- 

 tudes on a large scale, it would be a difficult matter to 

 draw the arcs representing the parallels of latitude 

 from the point representing the common centre of the 

 circles of whose circumferences these arcs form a part, 

 owing to the great length of the radii with which the 

 arcs must be described. It would be perfectly prac- 

 ticable, it is true, if we had our paper pinned down at 

 the end of a long table or board several feet in length, 

 and also had a beam compass wherewith to describe 

 the required arcs representing the parallels of latitude ; 

 but as these appliances are too costly to be bought by 



u 



301 



J30 



Fig. 18. 



any but professional draughtsmen and map engravers, a method 

 has been found by which parallels of latitude can be represented 

 by a number of short straight lines, arranged in such a manner 

 as to correspond very nearly with the circular arcs that would 

 properly represent the parallels of latitude. Our readers shall 

 be put in possession of this method of drawing parallels of lati- 

 tude when we show them how to make a projection for the 

 whole or any part of the British Isles. 



We will now show our readers a way by which they may fix 

 the position of any place on their projections, according to its 

 latitude and longitude, with great accuracy, and without the 

 trouble of making separate measurements for each place. That 

 this method may be clearly understood, we must ask our readers 

 to turn to Fig. 17 (page 356). 



The reader must suppose the figure in question to represent 



map, 



Having done this, paste at the back of the cardboard 

 a strip of tracing-paper, taking care to strain it 

 tightly ; and then place the strip over the projection, 

 so that the line a b in Fig. 18 falls exactly on the line 

 G H in Fig. 17 ; the line F E in the former coinciding 

 with the line F E in the latter. Now, thrust a draw- 

 ing-pin through the coinciding points, F, F, in each 

 figure, and moving the strip a little to the right or 

 left, so as to get the meridians of 15 and 20, or the 

 meridians of 20 and 25, in Fig. 17, showing through 

 the clear tracing-paper in the position shown by the 

 two thick meridian lines in Fig. 18, trace the paral- 

 lels from 75 to 30, and then subdivide the whole, 

 as shown by the dotted parallels and meridians in the 

 figure. The strip of cardboard will turn about the 

 point F as a centre, and on being turned so as to 

 bring the subdivided tracing-paper over any strip of 

 the projection bounded by two contiguous meridians 

 traced on the projection at a distance of five degrees 

 apart, will exhibit the strip beneath divided into spaces 

 each measuring a degree of latitude or longitude each 

 way. By moving the strip of cardboard as required, 

 the position of any place can be fixed on the projec- 

 tion with a pin or any sharp-pointed instrument. 



We will give the reader another method of fixing 

 the position of places according to their latitude or 

 longitude on his projection. Let him take a strip of 

 cardboard similar to that which is shown in Fig. 18, 

 but suited, of course, as far as length is concerned, to 

 the extent of his map from north to south. A portion 

 of the strip of cardboard marked G H c K. in the figure 

 must then be cut clean away, the line G K being in the 

 straight line drawn through E from the point F, the 

 centre from which the concentric arcs representing 

 the degrees of latitude have been described, and about 

 which the strip of cardboard must work. Having 

 secured the strip as before with a drawing-pin passing 

 through F, and also precisely through the point on 

 the paper underneath from which the parallels of 

 latitude have been described, let the edge of the card- 

 board, represented by G H, be laid against the central 

 meridian of the projection, and carefully graduated in 

 divisions, each representing a degree or a part of a 

 degree, if the projection be on a sufficiently large scale. 

 Having got a scale of degrees numbered along K G 

 from 30 to 75 (supposing that the map of Europe is 

 the map on which we are at work), which will indicate 

 the latitude of any place to be inserted in the map, by 

 moving it east or west from the central meridian as 

 required, the longitude may be fixed by bringing the 

 edge G K of the cardboard to the required longitude, 

 as shown in the graduated line at the bottom of the 

 in which is marked the longitude east and west from 



Greenwich, and the position of the place determined by making 

 a mark on the paper at its proper latitude, as shown on the gra- 

 duated line, G K. In using this method, however, care must be 

 taken to make allowance for the thickness of the point of the 

 pencil or steel-point with which the position of the place is 

 marked on the projection. 



These methods may be recommended as obviating the neces- 

 sity of subdividing the whole projection into spaces of a degree 

 each way, as shown in the centre of the lower part of Fig. 17. 

 The subdivisions of any strips of paper prepared as we have 

 directed for fixing the position of places on a projection accord- 

 ing to their latitude and longitude, must depend on the size of 

 the projection, and the length of the line assumed to represent 

 five degrees, two degrees, one degree, or even less, which is taken 



