672 Proceedings of the Royal Society of Edinburgh. [Sess. 
For greater convenience the values of e 0 are marked off instead of the values of e 0 /2. Because of 
this, and because the vertical scale is twice the horizontal, the angles made with the 
horizontal by the respective radial lines, are not the angles marked at the ends of these lines, 
but are equal to tan -1 (2 tan e 0 /2). 
= the number of vanes of the paddle-wheel. 
CHART III. 
