420 HOW MAPS ARE MADE. 



SO made is drawn and printed, and incidentally to sliow the use of the 

 various tools and instruments employed in these o[)erations, 



I assume that we all know that the earth is (roughly speaking) a 

 sphere, spinning round on its axis once in twenty-four hours. Now, if 

 we take up a sphere, like this ball, and mark a spot on it, there is noth 

 iiig whatever to define its position; no north, no south; nothing to 

 guule us. One ])0int on this si»here is the same as any other point, 

 until we liud some reference spot to measure from; but we have assumed 

 that we know that the earth spins round on its axis, and here we at 

 once discover something we can measure from. The ends of the axis 

 of the ball, which we call the poles, are, we see, at rest compared with 

 the rest of tlie surface of the si)inning ball. 



Now, this so-called polarity gives us at once two points of reference. 

 Although no one has ever been at either of the poles, the study of the 

 subject for hundreds of years has jiroNcd their existence as surely as if 

 the poles had been visited and been discovered marked with upstand- 

 ing posts. Between these two points, which we call the poles, L can 

 mark a point half-way, which, by spinning the ball in contact with the 

 pencil, I convert into a line called the equator, the equal divider, 

 popularly theWue. You will observe that this middle line, this eijuator, 

 is also the largest possible circle on this sphere, and it is from this circle 

 that all measurements and references north and south are made. We * 

 see on the globe and ou maps a number of other circles parallel to the 

 equator to the north and south of it, and drawn at equal distances. 

 These are called the parallels of latitude (or wideness), and they mark 

 certain degrees of angular divergence from the equator. 



Consider for a moment what this means. In the tirst conception of 

 them these lines have no sped tic distance apart, because they really 

 are angular measurements, and it is this conception of them I wish to 

 get h(»ld of. A degree of Uititude is not necessarily a number of miles, 

 and until we know the actual diameter of the earth we can not tell what 

 the length of a degree is. It is a proportion of the circumference of a 

 circle, a fractional measurement of it. We may speak of a half, a quar- 

 ter, of anything, but, until we say what it is a half or a quarter of, the 

 phrase conveys no idea of magnitude. It might be half a mile, or half 

 a kingdom, or half an inch, or half a crown. Similarly, a degree of a 

 circle means nothing so far as length is concerned, until you know the 

 size of the circle, when you can at once calculate, with the proper 

 mathematical knowledge, the numerical value of a degree at the earth's 

 circumference. 



Now, having marked these lines on the surface of the earth, we have 

 certain marks on our globe to which we can refer any and every point. 

 It may be said, " Why mark these lines on the map? They do not 

 exist; they are only imaginary." Quite true! But then the tirst prin- 

 ciple of all map-making is to begin with imaginary lines, from which 

 to measure the position of every place on that map; and all such imag- 



