24. This week select a blank space on the wall, or any other convenient spot, from where you usually sit, mentally draw a black horizontal line about six inches long, try to see the line as plainly as though it were painted on the wall; now mentally draw two vertical lines connecting with this horizontal line at either end; now draw another horizontal line connecting with the two vertical lines; now you have a square. Try to see the square perfectly; when you can do so draw a circle within the square; now place a point in the center of the circle; now draw the point toward you about 10 inches; now you have a cone on a square base; you will remember that your work was all in black; change it to white, to red, to yellow.
25. If you can do this, you are making excellent progress and will soon be enabled to concentrate on any problem you may have in mind.