registering the Variations of the Tide and Wind. 315 

 ing vertex of the tidal curve, and produce the line to the hour- 

 circle ; the point at which it cuts the hour-circle will indicate the 

 time required. The state of tide at any particular time of a gi- 

 ven day, is determined by drawing a line from the centre of the 

 dial, to the point in the hour-circle corresponding to the given 

 time, and measuring at what distance from the centre it cuts the 

 tidal curve for that day. 



The ordinary course of nature will produce uniformity in the 

 contour of the curves described, but any extraordinary occur- 

 rence will be strikingly indicated by a corresponding distortion. 

 For instance, suppose the face represented in Fig. 4. to have 

 been fixed to the dial-plate on the 1st day of a particular month, 

 we observe, that during nine days the curve follows a general 

 law, shewing that nothing extraordinary happened ; but we find 

 that, on the 10th day of the month, the tide rose 4 feet 6 inches 

 higher than was to be expected from the ordinary course of na- 

 ture, attained high water at S3 minutes past eight in the even- 

 ing, remained 57 minutes at its highest elevation, and then de- 

 scended 8 feet in the course of 20 minutes ; the subsequent low 

 tide appears to have taken place at 2 minutes past three in the 

 morning of the 11th, and fell 1 foot 9 inches below what was to 

 be expected ; and similarly, other extraordinary circumstances 

 would be indicated by a corresponding extraordinary feature in 

 the contour of the tidal curve. 



Fig. 5. represents a face supposed to be taken from the wind- 

 dial. To determine the direction of the wind at any particular 

 period, take a distance upon the scale (measuring from the cen- 

 tre) corresponding to the given time, and with that distance, as 

 a radius, describe a circle about the centre of the face. The in- 

 tersection of the circle with the wind-curve, will indicate the 

 point of the compass from which the wind blew at the given 

 time. As long as the wind blows steadily with a gentle breeze, 

 the fans placed in the box W will effectually prevent any violent 

 agitation from affecting the vane, and consequently the pencil 

 will describe a clear line. But it is intended, that if the wind 

 blow with regularity and considerable force, the vane may be 

 slightly agitated, in order that violent winds may be indicated 

 by some remarkable feature upon the wind dial-face, shewing us, 

 after considerable experience and observation of the action of 



