NOTICE.
Reading edition
In the pocket accompanying this work are two rings of stiff cardboard, on which will be found all the information contained in figures 1 and 2. When they are laid flatly upon a chart, the continuity of the lines on the chart is not materially interfered with, while the idea of a body of air rotating in the direction indicated by the arrows is conspicuously presented to the mind. These rings are more particularly referred to on page 52.