248 Col. Beaufoy on the Spiral Oar. [Oct. 



kind. The accompanying drawing, fig. 1, represents the spiral* 

 which consists of a double worm, a o, 20-8 inches in diameter* 



exclusive of the leaves, the cylinder d d round which it twines is 

 17-i. inches long; the parts a a are of brass, three inches broad; 

 the clock-work (not represented in the drawing) consists of a 

 pinion of 10 teeth fixed to the pivot of the axis d d, which gives 

 motion to a contrate wheel of 40 teeth fixed to an upright axis 

 passing in front of the frame ; at the bottom of the upright axis 

 is a small single thread worm, which turns a wheel of 50 teeth ; 

 on the axis of this wheel is fixed a long hand, which points out 

 200 yards in one revolution ; on the other axis is placed a pinion 

 of 10, which turns a wheel of 100, and shows, by a second 

 but smaller hand 2.000 yards, or nearly one nautical mile ; on 

 the other axis of this wheel is also a pinion of 10 teeth, which 

 communicates with another wheel of 100 teeth, and by another 

 index, or third band, shows 10 miles; on this axis, likewise, 

 there is a pinion of 10 teeth, which turns another wheel of 100 

 teeth, and by an index, or fourth hand, points out 100 miles. 



Fig. 2, represents a spiral log, the thick part of the machine 

 is of wood, for the double purpose of floating and fastening the 

 tin or copper leaves c c. If the spiral be truly made, and not 

 resisted in revolving, it is evident it will make one revolution or 

 half a revolution, whilst it moves through a space equal to the 

 length of its axis, one revolution if the twist make a whole turn, 

 half a revolution if the twist go only half round ; for the resisting 

 medium may be considered as a concave screw, and the spiral 

 as a convex one running into the former. To cut a plate of 

 metal the proper shape, it is necessary to have the dimensions 

 of the cylinder round which the metallic plate is to be bent. The 

 length of a spiral going half round the cylinder is equal to the 

 square root of the sum of the squares of the cylinder's length, 

 and half its circumference; and the diagonal of the cylinder is the 



