APPENDIX II 



CURVES AND MAPS 



444. Graphic Representations. Self-recording instruments, 

 like the barograph and thermograph, write their changes as con- 

 tinuous curves, which present to the eye a vivid picture of the nature 

 and extent of these changes. The daily and annual changes of tem- 

 perature and pressure are represented in the form of curves in Figs. 

 23, 24, and 28. When any one of the conditions under consideration 

 varies uniformly, the curve form of expression can be used ; thus 

 Fig. 27 shows temperature at different latitudes, where position 

 on the Earth varies uniformly, and Fig. 33 shows temperature at 

 various depths in the sea, where depth varies uniformly. The highest 

 point of a curve or any convex bend is called a maximum the lowest 

 point, or any concave bend, a minimum ; and a line drawn horizontally, 

 so that the curve cuts off an equal area above and below, is called its 

 mean. It is simply a matter of convenience that the space represent- 

 ing a degree of temperature, and that representing an hour, a day, a 

 fathom, or a degree of latitude, should have the same length in a 

 diagram. In the sections of oceans and continents there is a 

 natural relation between heights and lengths ; but if on a section of 

 Asia 100 miles of length were represented by an inch, the greatest 

 height of the continent would be shown by one-twentieth of an inch, 

 and would scarcely be visible. Accordingly heights are drawn on a 

 much larger scale, and the steepness of the slope is exaggerated in 

 the same proportion, while the positions and relative amounts of 

 change of level are brought vividly before the eye. It would be an 

 excellent exercise for the student to reduce these sections to a true 

 scale, either by reducing the heights on the paper to one-three-hun- 

 dredth of their height (but this is scarcely possible), or by keeping 



