314 Mr Allierton's Description of Machinery for 



a curve line upon the face of the dial. M represents the shaft 

 of the wind-vane, to which the wind-dial NO is fixed. A screw 

 is cut upon the shaft of the clock, which is supposed to turn 

 round once in twenty-four hours, and the pencil P being car- 

 ried by an arm projecting from the nut Q, nicely fitted to the 

 screw and shaft of the clock, it follows that, in the course of 

 twenty-four hours, the pencil is moved through a space equal to 

 the distance between two threads of the screw, and therefore 

 constantly moves at a uniform rate from the centre of the wind- 

 dial N O towards the circumference ; whilst, at the same time, 

 the variation of the wind causes the dial to revolve, by which 

 combined motions a curve-line will be traced upon the face of 

 the wind-dial. 



In order to make the wind-vane point steadily to the true di- 

 rection of the wind, and not subject to the constant vibrations, 

 and occasional pirouettes to which vanes, wanting some regulating 

 contrivance, are generally subject, a finely pitched wheel R S, 

 is fixed to the vane-shaft, which wheel, working into the pinion 

 T V, causes fans to revolve in the close-box W, filled with fluid. 

 The resistance thus opposed to any sudden and violent motion 

 of the fans, will cause the vane to move steadily. But the re- 

 sistance to the fans, when moving in the fluid with a slow steady 

 motion, will be so small as not to afifect, in any sensible degree, 

 the truth with which the vane would indicate the direction of the 

 wind. 



Fig. 3. is a view of the face of the machine, the pannel being 

 removed. The letters on fig. 3 are placed agreeably to fig. 2. 



Fig. 4. represents the face of the tide-dial, with a supposed 

 tidal curve traced upon it, in half a lunation, or in the interval 

 between the new and full moon. In practice, the dial is sup- 

 posed to be 3 feet in diameter, and the rise of an ordinary 

 spring-tide from low to high water mark 20 feet, which lineal 

 motion, being reduced by the wheel and pinion turned by the 

 float, is here arranged so as to move the pencil through the space 

 of 10 inches. Therefore, as the tide rises or falls 1 foot, the 

 pencil would ascend or descend \ inch. At each time of tide, the 

 curve will form a vertex. If we wish to determine the time of 

 high or low water for any particular tide, we have to draw a 

 straight line from the centre of the dial, through the correspond- 



