TRENCHING AND SUBSOILING. 



155 



As all parts of the vanes do not revolve at the same speed, 

 the chord of the parabolic segment of the section forms 

 an angle of 32 towards the centre, and 1 2 only towards 

 the periphery, with the plane perpendicular to the axis of the 

 motor. 



The curve of the vanes is secured by four pieces of ash- 

 wood j^jxl^- inch section, drawn in the required curve, 

 and nailed under each vane at distances of 3ft. 3in. apart. 

 The part of the vane resting on the circles M M' M" is 

 faced with zinc. 



The motor is, therefore, a regular polygon, with 32 

 sides, and a diameter of 26ft. 3in. If the vanes are pro- 

 jected on a plane perpendicular to the axis they overlap 

 each other to the extent of ^ inch only, and in the 

 centre there will be a circular opening 8 inches in diameter. 

 The vanes have also lengthwise a curvature of \\ inch to 

 utilize the centrifugal force developed by the rotary move- 

 ment. 



The mode of attachment of the vanes allows the sailing 

 area to be regulated according to the strength of the wind, 

 in the ratio 1:16, by removing some of the vanes two by two 

 on the same diameter, so as not to disturb the equilibrium, of 



