218 FIRST YEAR COURSE IN GENERAL SCIENCE 



the lines, would be twenty feet. The zero-foot line and the 

 twenty-foot line would come nearest together at the steepest 

 place. 



239. Illustration of Contour Lines and Intervals. To 

 illustrate the use of contour lines in showing the form of 

 the land, suppose that a cone measuring three inches high 

 and three inches across the base is cut into three sections 

 of equal thickness, parallel to the base. A long pin or wire 

 is passed through the center of the three sections. The 

 cone is placed upon paper and the outline of its base is 

 drawn. It is a circle. The lower section is removed, and 

 the remainder of the cone is placed upon the paper with the 

 center where it was before. Its outline is another circle 

 smaller than the first. Continuing the work, we get a circle 

 of the size of the base of the upper section. A dot at the 

 center represents the top of the cone. Number the circles 

 from the outer one, 0, 1, 2. 



Make a diagram of the front view (profile) of the cone, 

 showing the horizontal sections. On the side of the profile 

 number the base 0, the first line 1, and the second line 2. 

 Compare the cone with the diagram. The base of the cone 

 is inches above the table. The circle is the contour line 

 of inches. The first section of the cone is 1 inch above 

 the table; the circle 1 is the contour line of 1 inch. The 

 contour interval, the vertical distance between them, is 1 

 inch. Compare other points on the cone and on the circles. 



Now let this cone represent a cone-shaped volcano, the 

 contour interval of which is 500 feet (that is, 1 inch on the 

 cone represents 500 feet). State the height of the volcano 

 above the level 0. Name the contour line which represents 

 an elevation of 1,000 feet. 



The length of the line represents horizontal distance, and 

 the diameters of all the circles represent horizontal dis- 

 tances. The base of the cone extends three inches from 

 east to west, three inches from north to south. The point 1 



